Viral Features Archives - Kickstart Side Hustle

Hooked Model Details

Hooked Model explains how habit-forming products keep people coming back by running them through a simple loop: trigger, action, reward, and investment. Each pass through the loop strengthens the behavior, building habits and sometimes even creating compulsive use.

The Hook Model loop has four components:

Triggers:
- External Trigger- what external cues get the user to the product?
- Internal Trigger- what motivates the user?
Action - what is the easiest action for the user to receive the reward?
Variable Reward (Motivating-Uncertainty Effect + Variable-Ratio Schedule) - is the reward fulfilling, yet leaves the user wanting more
- Variable Rewards of the Tribe - what changing social feedback pulls the user back?
- Variable Rewards of the Hunt - what new thing can the user find each time?
- Variable Rewards of the Self - what small win or progress feels different each time?
Investment - Ikea Effect

Think of opening a social app because you’re bored. You scroll, see something surprising, and then maybe leave a comment or like a post. That small bit of effort trains the app to show you better content next time, and makes you more likely to return.

In marketing this model shapes notifications, habit loops, personalization, and small user investments that deepen attachment. When the cycle repeats smoothly, the product becomes part of daily life.

Basically, repeated loops create habits, and can slide into addiction.

Hooked Model Guide

Start with clear triggers
Triggers pull people into the loop.
- External triggers: things outside the user that call them in.
  Examples: notifications, emails, reminders, signs, messages.
- Internal triggers: emotions or states inside the user.
  Examples: boredom, stress, curiosity, loneliness, desire for progress.
  The strongest habits form when the product connects to an internal trigger.
Make the action the easiest possible step
The user should be able to act without thinking. One tap, one swipe, one glance, one small task. If the action feels heavy, the loop breaks. If the action feels effortless, the loop grows.
Give a variable reward that feels good but not complete
Variable rewards work because of the Motivating-Uncertainty Effect - the brain pays extra attention when it doesn’t know exactly what it will get.

This follows the Variable-Ratio Schedule - rewards appear after an unpredictable number of actions (sometimes quickly, sometimes later).
This schedule creates the strongest habits known in psychology.

A good variable reward satisfies the user just enough, but still leaves a desire for “one more try.”

Now the 3 reward types:
- Variable Rewards of the Tribe - social rewards
  Examples: likes, comments, shares, reactions.
- Variable Rewards of the Hunt - searching and finding
  Examples: infinite scroll, recommended videos, new updates, discounts.
- Variable Rewards of the Self - personal progress
  Examples: finishing a level, beating a score, completing a task, unlocking something.
Add a small investment that improves the next experience
After the reward, ask for a tiny investment - a choice, a preference, a saved item, a bit of content, a setup step.

This creates the IKEA Effect: people value what they helped create.
The next time they return, the product is better because of what they added.
Let each loop strengthen the habit
Triggers get stronger.
Actions get easier.
Rewards feel more personal.
Investments stack up.
This makes the loop feel automatic.

Hooked Model Research

Research 1 - External Trigger - External triggers kick off habits

Research in behavioral design shows that the very first “nudge” that leads to a habit often comes from outside us (an external cue) rather than just internal feelings.

Nir Eyal notes that in his “Hook Model” framework, triggers are the first step: an external trigger (push notification, email, banner, icon) signals “do this now”. Over time, what begins as external is internalised (i.e., the user starts acting without the push).

Nir Eyal mentions four kinds of external triggers in his book:

Paid triggers - Advertising and paid marketing that attract people to check out a product or service.
Earned triggers - Press, viral videos, App Store rankings, SEO. Very effective but hard to replicate.
Relationship triggers - Referrals and word of mouth. Using relationships to reach a new audience.
Owned triggers - A part of your user’s environment by their own choice: the app icon on home screen, an email newsletter, or push notifications.

External triggers only work when they’re tightly linked to an internal trigger (an emotional itch, boredom, loneliness, uncertainty) and when the user is ready (has ability + motivation). If the external cue hits without the emotional itch/ready state, it fails or feels “spammy”

Research 2 - Internal Trigger - Internal triggers get us into habits

Behavioral psychology shows that around 90% of the time we get distracted or engage in a habit, it’s due to internal triggers (feelings) rather than external prompt.

Nir Eyal notes that studies found people blame their phone notifications for distraction, but actually most device-checking is self-initiated because of an internal urge.

One research finding is that when people are bored, they reflexively reach for their phones to fill that void. Tech companies are aware of this: we’ve seen product metrics indicating peak engagement at times people are likely bored or lonely, like late evening scrolls, Monday morning commutes,

Research 3 - Motivating-Uncertainty Effect - Mystery rewards make people try harder

Research that studied monetary prizes in two situations - when the prize is unknown and can vary from small to very large, and when the prize is a known amount– showed that people were much more likely to be stimulated by the unknown. The summary was that people were more motivated by tasks with an unknown reward:People had to drink a big amount of water in 2 minute.\

Group A: guaranteed $2
Group B: random reward of $1 or $2

Results:

Group A: 43% finished
Group B: 70% finished

That’s a 63% boost just because the reward was uncertain.

Research 4 - Variable-Ratio Schedule - Pigeons work harder for random time rewards

This idea comes from B.F. Skinner’s experiments. He learned that pigeons peck a button way faster when the reward comes at random times. In one study, every bird pecked more under a variable-ratio schedule, even though they actually got fewer treats than birds on a predictable schedule. So the pigeons worked harder for random rewards than for regular, more frequent ones.

Research 5 - IKEA Effect - Building the item made people value it 63% more

One research found that even if participants had built a simple IKEA storage box by themselves, they were willing to pay 63% more for it, compared to a group of people who only saw the fully built.

Hooked Model Examples

1. Strava

Trigger: a friend likes or comments on your run.
Action: you open the app to check the notification.
Reward: you get social approval (likes, kudos, comments).
Investment: you upload another workout, making future rewards more likely.

Every posted run increases your identity investment, so you keep coming back to protect your streak, your stats, and your public persona. The more you log, the harder it is to quit.

2. Tinder

Trigger: boredom >> open Tinder.
Action: swipe left or right.
Reward: variable - sometimes nothing, sometimes a match.
Investment: messages, matches, profile tweaks >> increasing future match chances.

Feedback Loop Details

Feedback Loop means one action creates a result, and that result shapes the next action. The cycle repeats and guides the system in a clear direction.

Think of a product getting great early reviews. Good reviews bring more customers. More customers create more good reviews. The loop grows and speeds up. That’s a positive feedback loop - momentum feeding more momentum.

Now think of a system that stops problems from growing. A drop in customer satisfaction triggers support alerts, support fixes the issues, satisfaction rises again. The loop pushes things back to normal. That’s a negative feedback loop - it pulls the system back into balance.

In marketing both loops matter. Positive loops drive growth, virality, and compounding results. Negative loops keep quality steady, protect trust, and stop small issues from turning into big ones.

Basically, positive loops speed things up, negative loops keep things under control.

Feedback Loop Guide

Build strong positive feedback loops
When a user does the right thing, reward it fast. A quick win, visible progress, or a small dopamine hit makes the behavior repeat. Positive loops create momentum, habit, and long-term engagement.
Use negative feedback loops to prevent bad outcomes
Negative loops gently slow or stop unwanted behavior. Clear warnings, error states, or corrective nudges help users adjust without punishing them. Negative loops stabilize the system and keep users on track.
Keep feedback instant and obvious
Fast feedback teaches the brain what works. Slow or hidden feedback kills confidence and creates confusion. The shorter the loop, the faster the learning.
Balance simplicity with clarity
Do not oversimplify the interface so much that signals disappear. Users need to feel cause and effect. Lack of feedback creates anxiety, mistakes, and broken loops.
Let beginners get simple signals and pros get deep signals
Start with clean confirmations for new users. Offer detailed metrics, logs, or insights for experts. Shallow loops block mastery; deep loops enable growth.
Make every feedback event point to a next action
A good loop never dead-ends. Each signal should smoothly guide the user to continue, correct, or level up. Loops are not messages; they are directional nudges.

Feedback Loop Research

Research 1 - Feedback loops shape new behaviors

Before the experiment, households only received a monthly electricity bill - a big, delayed summary of what they did weeks earlier, offering no real-time guidance or motivation to change.

The researchers then installed real-time energy displays in these homes with small screens placed in visible areas that showed current electricity use and, in some versions, the exact money being spent or saved moment by moment. This let people see the immediate effect of their actions.

The results showed that households cut electricity use by about 15% on average, with reductions reaching up to 20% in the first weeks. Displays showing money saved produced even stronger effects than those showing only kilowatt-hours.

Feedback Loop Examples

1. Figma

Figma builds a product feedback loop by using community feedback, feature requests, beta testing and community discussions. They collect user input, then use that to shape updates, new features and improvements.

2. Whoop (fitness band)

Whoop creates a closed feedback loop. While you train, the app gives you a strain score, for your sleep it gives you a Recovery Score, etc. Low recovery instantly nudges you to adjust your next-day behavior, and when your score improves, it reinforces trust in the device. Over time this loop becomes addictive, making people stay subscribed because they feel they can’t manage their training without those daily numbers.

Curiosity Gap Details

Curiosity Gap means we feel a strong pull to fill in missing information. When we see a hint without the full answer, our brain wants to close the gap.

Think of reading a headline that teases a surprising fact but doesn’t give the full story. You click because the missing piece bothers you just enough to take action.

In marketing this gap drives engagement. Teasers, questions, partial reveals, and open loops make people lean in because they want to know what comes next.

Curiosity Gap Guide

Reveal just enough to spark the tension
The curiosity gap opens when you give a hint, not the answer. A small piece of information creates an itch the brain wants to scratch. Too much detail kills intrigue; too little kills understanding.
Highlight the unknown, not the known
Point attention at what people don’t know yet. A hidden benefit, a surprising twist, or an unexpected result pulls the mind forward. The brain cannot ignore unfinished ideas.
Use open loops (Zeigarnik Effect) that promise resolution
Story fragments, cliffhangers, and unanswered questions make people thinking about it even later.But an open loop without payoff breaks trust.
Types of Curiosity Gaps
- information gap (the classic)
  You reveal part of the story but hide the key detail.
  example: “A teacher asked her class one simple question. What happened next surprised everyone.”
- knowledge gap
  You imply that the reader is unaware of something important.
  example: “Most investors overlook this one metric, and it’s costing them millions.”
- emotional gap
  You trigger an emotion but don’t reveal the cause.
  example: “This 12-second video made an entire courtroom cry.”
- expectation violation gap
  You set up a familiar scenario, then hint that something unexpected happened.
  example: “He opened the package expecting headphones. What was inside left him speechless.”
- social comparison gap
  You show that others know/do something that the reader doesn’t.
  example: “Why top athletes avoid this common morning habit, and why you probably don’t.”
- competence gap
  You hint that experts outperform others for a hidden reason.
  example: “The world’s best designers follow one rule when choosing colors. Most beginners ignore it.
- mystery gap
  You present an unexplained phenomenon and promise an answer.
  example: “Scientists finally solved a 40-year-old puzzle, and the explanation is wild.”

Curiosity Gap Research

Research 1 - A small tease doubled choices for the mystery prize over cash

In a study from 2007, people chose between a sure thing (cash) and a mystery prize. When the researchers gave them just a little information about the mystery box (not the whole truth), curiosity shot up. People became more than twice as likely to choose the unknown prize instead of the cash. That small tease created a curiosity gap, and the urge to learn the missing info pushed them to take the risk.

Research 2 - The best clicks happen when headlines reveal a little and hide a little

A large analysis of 8,977 headline A/B tests found that headlines with an optimal “curiosity gap” achieved the highest CTR.

Upworthy’s data showed that only ~9% of very vague headlines gained clicks by adding info, whereas over 50% of overly detailed headlines actually saw ~5–10% fewer clicks.

This supports Loewenstein’s information-gap theory: headlines that leave readers guessing (not too little, not too much) can boost engagement.

Research 3 - Curiosity-gap subject lines drive +33% opens

Research on email marketing showed that using curiosity gap can lift open rates. In one study, 33% of recipients opened an email solely due to a compelling, curiosity-inducing subject line. Adding personalization further amplified this effect - personalized, curiosity-gap subject lines saw open rates climb by ~35%.

Curiosity Gap Examples

1. Hathaway shirts

Ogilvy put a cheap eye-patch on a perfectly normal model wearing Hathaway shirts. This made people instantly curious about the model.

The first ad ran in The New Yorker in 1951. Within a week, every Hathaway shirt in New York was sold out.

2. Curiosity - “What’s Inside the Cube?” (game)

The game showed one giant cube with billions of tiny blocks, and nobody knew what was hidden inside.

Millions joined just to tap cubelets and see “what’s in the middle.” The mystery was the whole engine of the game.

The curiosity gap was so strong it millions of people started to play. The traffic even crashed servers.

3. Heyah (Polish telecom)

In 2004, Heyah flooded cities with a strange red hand logo and a website called “nadchodzi.pl” (“it’s coming”) - but didn’t reveal the brand.

People kept asking “What is this? Who is behind it?” The curiosity gap exploded, driving 1.2M unique visitors before launch.

When the reveal finally came, Heyah got over 300k users within the first month.

Zeigarnik Effect Details

Zeigarnik Effect means our brains remembers unfinished tasks better than completed ones. Open loops stick in memory and keep pulling our attention back.

Think of starting a show and stopping halfway through an episode. Your mind keeps nudging you to return, simply because the story isn’t done.

Cliffhangers, teasers, half-revealed info, or progress bars make the brain want to finish what it started.

Zeigarnik Effect Guide

Use curiosity to drive action
Start your ad or headline with a question the reader feels they need to answer.
Use progress bars everywhere
In sign-ups, onboarding, quizzes, and checkouts, show something like “Step 2 of 5.” People feel the urge to complete it.
End content with a hook
At the end of an email or video, tease the next thing. This keeps people coming back.
By combining more hooks throughout the sales copy or by revealing small bits of the puzzle at a time, your copy is able to engage the viewer deeper and deeper into the sales process.
Don’t overdo it
Make sure the loop closes quickly. If you drag it out or make the next step too hard, it stops being intrigue and starts being annoying.
Create open loops
Create open loops in your content. By combining more loops throughout the sales copy or by revealing small bits of the puzzle at a time, your copy is able to engage the viewer deeper and deeper into the sales process.

The "slippery slope" is a copywriting technique that uses the Zeigarnik Effect to connect the paragraphs to the next paragraph.

“Next…”
“In a moment, I will tell you about…”
“Last but not least…”
"Moreover..."
"Next..."
"There’s more..."
"Let me explain..."
"Here’s how..."

These and alike are phrases that help you keep the proper level of attention in your readers. They may be called “linkers,” and they not only make your text more interesting but also more readable.

Zeigarnik Effect Research

Research 1 - We remember interrupted tasks 90% better than completed ones

In 1927, Bluma Zeigarnik observed the effect first in a restaurant: waiters could remember complex food orders, but once customers got their food and paid their bill, all details were forgotten.

Then Bluma tested the idea. She gave participants several small tasks like puzzles or building simple objects. Half the time she interrupted them, and half the time she let them finish normally.

Afterward, she asked everyone what they remembered. People recalled the interrupted tasks about 90% better than the ones they completed without interruption.

Zeigarnik Effect Examples

1. YouTube

YouTube auto-play the next episode or video, often not even letting the credits finish – this leaves the narrative hanging just enough that your brain says “well, maybe just one more.” Binge-watching thrives on this principle.

2. Duolingo

Dolingo shows a streak meter or a lesson tree with locked levels, so you always have an unfinished goal compelling you to come back tomorrow

Internal Trigger Details

Internal Trigger means a feeling inside us pushes us to take action. It comes from emotions like boredom, stress, loneliness, or curiosity, not from anything outside.

Think of grabbing your phone without any notification. You acted because you felt bored or restless for a moment. The emotion was the trigger.

In marketing internal triggers shape habits. When a product fits a recurring feeling, people return on their own without reminders or ads.

Internal Trigger Guide

Connect to a feeling
Figure out the main emotion behind using your product (boredom, FOMO, stress, curiosity). Show clearly how your product solves that feeling, so people naturally think of you whenever it hits.
Build habits
Match your content or features to moments when users already feel a specific internal trigger. If people crash at 3pm, drop your helpful post or feature then. Over time, they’ll come to you automatically without reminders.
Fix pain or give a quick reward
Internal triggers are usually about stopping discomfort or getting a small hit of pleasure. Make your product fast, easy and reliable so it becomes the natural go-to.
Speak like their inner voice
Use simple, direct copy that matches what people think in the moment, so they link a situation to your product in their head.
Avoid toxic loops
Don’t lean on harmful triggers or fuel insecurity. If your product supports people during negative emotional moments, it should genuinely help, not create dependency.

Internal Trigger Research

Research 1 - Internal triggers get us into habits

Behavioral psychology shows that around 90% of the time we get distracted or engage in a habit, it’s due to internal triggers (feelings) rather than external prompt.

Nir Eyal notes that studies found people blame their phone notifications for distraction, but actually most device-checking is self-initiated because of an internal urge.

One research finding is that when people are bored, they reflexively reach for their phones to fill that void. Tech companies are aware of this: we’ve seen product metrics indicating peak engagement at times people are likely bored or lonely, like late evening scrolls, Monday morning commutes,

Internal Trigger Examples

1. Snickers

Snickers’ “You’re not you when you’re hungry” campaign essentially tried to establish hunger (and the irritability it causes) as an internal trigger to buy Snickers. They humorously pointed out that emotional state and linked their product as the solution.

2. Pepsodent (Claude Hopkins)

Claude Hopkins told people there’s a thin film on their teeth and made them check it with their tongue. That little feeling became the internal trigger.

Whenever someone noticed that film, they automatically thought about brushing with Pepsodent.

Within a few years, daily brushing exploded across the country - from 7% to 65%.

External Trigger Details

External Trigger means something outside of you prompts you to act. It’s a cue you see or hear that pulls your attention and tells your brain what to do next.

Think of hearing your phone ping and instantly checking it. The sound, not your feeling, started the action.

In marketing external triggers guide behavior. Notifications, ads, emails, pop-ups, and clear calls-to-action remind people you exist and show them the next step.

External Trigger Guide

Use triggers to prompt key actions
Map the user journey and place reminders where people typically drop off. A follow-up email after an unfinished onboarding or a push when new content appears can guide users back into the next step. External triggers give the first gentle push.
Add the behavioral science foundation
Research in behavioral design shows that the first nudge that starts a habit usually comes from the outside. Nir Eyal’s Hook Model starts with external triggers: a cue like a push, email, banner, or icon that tells the user to act. Over time, these external cues become internalised, and users start acting on their own without being pushed.
Know the four types of external triggers
- Paid triggers: ads and paid campaigns that pull people in.
- earned triggers: press, rankings, SEO, viral moments. Hard to engineer but very powerful.
- relationship triggers: referrals and word-of-mouth.
- owned triggers: things the user has allowed into their environment, like an app icon, newsletter, or push notifications.
Make triggers clear and specific
A good trigger tells the user exactly what to do and why it matters. Clear wording tied to user value always beats a generic prompt. Specific cues create higher response rates and lower confusion.
Nail timing and context
A well-timed trigger feels helpful. A badly timed one feels like spam. Use data on time of day, behavior, or location to send triggers when they’re welcome. Meal kit apps remind users to pick meals right before the cut-off, not at random moments. Context boosts relevance.
Don’t overload users
Too many reminders lead to mute, unsubscribe, or delete. Fewer, high-value triggers work better than constant nudges. Segment your audience, personalise messages, and watch opt-out rates to spot trigger fatigue early.
Link external triggers to internal ones
External triggers work only when they connect to an internal itch like boredom, loneliness, uncertainty, or curiosity. And when the user has enough motivation and ability to act. If the internal itch isn’t there, the trigger feels useless or annoying.
Use external triggers to build internal habits
At first, strong external cues help users form routines. A daily morning reminder to exercise can set the pattern. After a few weeks, the time of day becomes the built-in internal cue. The goal is that the habit continues even without the external push. External triggers start the process; internal triggers sustain it long-term.

External TriggerResearch

Research 1 - External triggers kick off habits

Nir Eyal mentions four kinds of external triggers in his book:

Paid triggers - Advertising and paid marketing that attract people to check out a product or service.
Earned triggers - Press, viral videos, App Store rankings, SEO. Very effective but hard to replicate.
Relationship triggers - Referrals and word of mouth. Using relationships to reach a new audience.
Owned triggers - A part of your user’s environment by their own choice: the app icon on home screen, an email newsletter, or push notifications.

Research 2 - External Triggers like notifications, work too well

Companies track how well triggers work by looking at things like CTR and conversions. Push notifications are one of the strongest triggers. Data shows that apps with push switched on keep about 65% of users active after 30 days, while apps without push keep far fewer.

Push also boosts engagement users who get notifications can be up to 88% more active than users who don’t.

External Trigger Examples

1. Duolingo

Duolingo’s owl sends you a daily push that mixes guilt and encouragement. It’s a simple external trigger, but it works. People open the app and keep their daily streak going.

2. LinkedIn

LinkedIn sends external triggers in emails like “5 people viewed your profile - see who!” which lures you back to the platform via curiosity.

FOMO Effect Details

FOMO is the fear of being left behind. It's your brain’s alarm for not missing out. It’s that quick fear that others are getting something good and you’re not.

It’s not logic, it’s old survival wiring. Long ago, missing what the tribe had could mean less food or safety. Today, it’s just seeing others win online and feeling behind.

Think of scrolling social media where everyone’s on trips, launching things, looking happy, and you suddenly feel the need to catch up. That’s your brain pushing you to act fast.

In marketing, FOMO works like fuel. Phrases like limited stock, last chance, or everyone’s already in trigger that fear and make people decide quicker.

Your brain’s fear center lights up when you think you’ll be left out, so you rush to join.

FOMO Effect Guide

Use urgency
Tell people when your offer ends or show a countdown. Real deadlines make people act fast.
Use scarcity
Point out limited stock or spots left.
Show social proof
Let others see what people are doing. Show recent purchases or how many people have already joined. When people see others taking action, they feel the need to join too.
Create exclusivity
Make offers feel special, like early access, VIP deals, or bonuses for the first customers. Feeling part of a select group increases engagement and signups.
Be real about FOMO
Avoid fake timers or false scarcity, as they destroy trust. Real limited offers work much better. People hate missing out, so make your offer something worth acting on.

FOMO EffectResearch

Research 1 - A countdown timer can boost sales by 226%

The online retailer tested a limited next-day shipping offer against another version in which the limited offer wasn’t shown.

The limited-time shipping offer boosted sales by 226%! All it took was one line of text with a countdown.

Research 2 - FOMO is everywhere

FOMO drives about 60% of total sales today.
60% make a purchase within 24 hours of feeling FOMO
81% of millennials buy products after seeing friends’ posts.

FOMO Effect Examples

1. The Dutch postal code lottery

To win the prize of the Dutch postal code lottery (the largest charity lottery in the Netherlands) person needs to buy a ticket and reside under the postal code drawn.

People who didn’t buy a ticket but could have won the lottery will be notified.

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2. Booking

Booking.com has multiple examples of FOMO on every page. Booking.com is showing the visitors that they have actually missed out on a great deal.

Category Archives: Viral Features

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Research 1 - External Trigger - External triggers kick off habits

Research 2 - Internal Trigger - Internal triggers get us into habits

Research 3 - Motivating-Uncertainty Effect - Mystery rewards make people try harder

Research 4 - Variable-Ratio Schedule - Pigeons work harder for random time rewards

Research 5 - IKEA Effect - Building the item made people value it 63% more

2. Tinder

Research 1 - Feedback loops shape new behaviors

2. Whoop (fitness band)

Research 1 - A small tease doubled choices for the mystery prize over cash

Research 2 - The best clicks happen when headlines reveal a little and hide a little

Research 3 - Curiosity-gap subject lines drive +33% opens

3. Heyah (Polish telecom)

Research 1 - We remember interrupted tasks 90% better than completed ones

2. Duolingo

Research 1 - Internal triggers get us into habits

2. Pepsodent (Claude Hopkins)

Research 1 - External triggers kick off habits

Research 2 - External Triggers like notifications, work too well

2. LinkedIn

Research 1 - A countdown timer can boost sales by 226%

Research 2 - FOMO is everywhere

2. Booking