Behavioral economics & viral marketing case studies
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:
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
Hooked Model 
Research
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:
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”
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 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.\
Results:
That’s a 63% boost just because the reward was uncertain.
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.
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.
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.
Commitment & Consistency Details
Commitment & Consistency Bias means once we commit to something, even in a small way, we feel the need to stay consistent with that choice. Changing course feels uncomfortable.
Think of agreeing to go to a Thursday 6 PM training session with a friend. After showing up once, you feel pushed to keep going every Thursday, not because the workout changed, but because you already committed to that specific slot and want to stay consistent with it.
In marketing this bias powers small onboarding steps, micro-commitments, quizzes, and simple one-click starts. Once people take the first step, they naturally follow through.
Commitment & ConsistencyGuide
Commitment & ConsistencyResearch
In the study from 1966, the researchers asked women to do a small favor - answer a few questions about the cleaning products they used. It was an easy, non-invasive request.
Three days later, the same women received a much bigger request - they were asked to let researchers into their homes for about 2 hours to check all their household products.
The result:
This well-known example, often mentioned by Robert Cialdini, tested how a tiny change in wording could reduce restaurant no-shows.
That small shift, from giving an instruction to getting a simple verbal promise, cut no-shows from 30% to 10%. It showed how even a tiny commitment makes people much more likely to follow through.
Commitment & ConsistencyExamples
1. Audible
Audible forces you to pick your first audiobook the moment you join. Once you choose a book, you psychologically commit to listening. This simple step massively boosts first-month retention.
When you click “Save for later,” Amazon treats this as a micro-commitment. You feel like you’ve chosen the item mentally, so buying it later feels consistent with your previous decision. This is why Amazon keeps those items visible forever - you already committed once.
IKEA Effect Details
IKEA Effect means we value things more when we’ve put effort into making them, even if the final result isn’t perfect. Effort creates attachment.
Think of assembling a simple shelf at home. It might look a bit crooked, but because you built it yourself, it feels more special and harder to throw away than a similar one bought pre-assembled.
In marketing this bias shows up in customization tools, build-your-own kits, quizzes, and products that let people co-create the final outcome. When customers invest effort, their perceived value goes up.
IKEA Effect Guide
IKEA EffectResearch
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.
IKEA Effect Examples
1. Nike By You
Nike’s Nike By You lets customers design their sneakers: colors, materials, engraving. People value these shoes far more than regular ones, even if the quality is identical. The effort of customizing makes the final product feel premium and emotionally important - pure IKEA Effect.
Notion doesn’t give you a rigid structure, you build your own system: pages, databases, templates. People overvalue their messy, homemade setups because they made them. The more time someone spends constructing it, the harder switching apps becomes (huge retention effect).
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
Feedback Loop Research
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.
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.
Pseudo-Set Framing Details
Pseudo-Set Framing means we get motivated when tasks feel like part of an incomplete set, even if the set is totally made up. Our brain hates leaving things unfinished.
Think of loyalty cards that start you off with a few stamps already filled. You suddenly feel closer to completing the set, so you push harder to finish it, even though the extra stamps were artificial.
In marketing this bias drives progress bars, starter points, checklists, and reward systems. When people see themselves as partway through a set, they’re more likely to keep going.
Pseudo-Set Framing Guide
Pseudo-Set Framing Research
Website 1
Website 2
Website 3
The HBS pseudo-set framing research was tested in the real world with the Canadian Red Cross during its 2016 holiday fundraising campaign.
Over 7,000 donors were randomly sent to one of three pages:
The effect was huge: 21% of people in the pseudo-set condition donated the entire six-item kit, compared to only 5% in the gift condition and 3% in the cash condition. That's roughly a 320% increase in full-completion behavior. Simply showing the items as a “set” made people far more likely to finish it.
Pseudo-Set Framing Examples
1. LinkedIn - Profile Strength Meter
LinkedIn breaks your profile into a set of 5-7 pieces (photo, headline, experience, skills, summary, connections, etc). These elements don’t actually need to be treated as a set, but framing them together with a progress bar creates urgency to complete the full set. This pseudo-set framing makes users finish their profiles far more often.
H&M dresses mannequins in a full outfit. Usually 5-7 items like a jacket, shirt, pants, shoes, and accessories. Even though each item is sold separately, the outfit looks like one complete set in your mind. Because of this, many shoppers try to buy the whole outfit, not just one piece.
Sunk Cost Effect Details
Sunk Cost Effect means we keep investing time, money, or energy into something just because we’ve already put a lot into it, even when quitting would be smarter. The past effort traps us.
Think of staying in a bad project just because you spent months on it, even though it doesn't earn any money. Or you're stuck in a bad relationship even though you don't love the other person anymore. The time you already invested pulls you in, not the actual value.
In marketing this effect keeps customers subscribed, committed, or loyal to things they’ve already paid for or spent effort on. The more they’ve put in, the harder it feels to walk away.
Sunk Cost Effect Guide
Sunk Cost Effect Research
In a 1985 study by Arkes and Blumer, people got theatre tickets at different prices:
54 people who paid more for a theater season pass ended up going to more shows over 6 months, just to use their pricey ticket. The cheaper the ticket, the less likely people were to use it.
Sunk Cost Effect Examples
1. Starbucks rewards
Starbucks gives you points that expire. When you have something like 70/100, you don’t want that effort to go to waste. So you buy another coffee or two just to “finish the set.” The more points you’ve collected, the stronger the pull.
People spend thousands on the Peloton bike. After that, they feel they must keep the monthly subscription active, or else that big investment feels wasted. The high upfront cost keeps them inside the system much longer.
Motivating-Uncertainty Effect Details
Motivating-Uncertainty Effect means not knowing the exact reward can make us work harder than when the reward is guaranteed. The mystery creates excitement and keeps the brain engaged.
Think of doing extra tasks in a game just for a chance at a mystery box. You don’t know what’s inside, but the uncertainty makes the effort feel more fun and energizing than a fixed prize.
In marketing, this means surprise bonuses, mystery gifts, and unpredictable wins keep people coming back because the next reward might be even better.
The key difference from a Variable-Ratio Schedule is that motivating-uncertainty focuses on the mystery of the reward itself, while variable-ratio is about unpredictability in when the reward appears.
Motivating-Uncertainty Effect Guide
Motivating-Uncertainty Effect Research
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 minutes.
Results:
That’s a 63% boost just because the reward was uncertain.
Mystery discounts beat normal discounts. Brands like GAP and Banana Republic send emails saying “Click to see your secret discount – maybe 15%, 30%, or even 50%.”
Shoppers were more likely to buy when there was a 10% chance the item was free than when everyone got a guaranteed 10% off.
Supermarkets saw the same thing. Customers preferred a “1% chance your whole cart is free” lottery over a normal 1% discount.
Motivating-Uncertainty EffectExamples
1. Loot boxes
Instead of giving players a guaranteed prize for a challenge, games often give a loot box with random items. Players end up playing more and even paying money for these boxes, chasing the excitement of a rare find.
Every time you buy certain items, you peel a sticker, and you don’t know if it’s a free fries, a drink, a rare piece, or a big prize.
Most prizes are tiny, but the uncertainty is what drives the motivation. People buy more meals because each peel feels like a small gamble with suspense, even if the expected reward is low.
Variable-Ratio Schedule Details
Variable-Ratio Schedule means rewards appear after an unpredictable number of actions. The uncertainty keeps the brain hooked because the next win could happen at any moment.
Think of pulling a slot machine lever. You might win on the third pull, the tenth, or the fiftieth. The randomness makes you keep going, chasing the next hit.
Apps, games, and loyalty systems use unpredictable rewards to keep people checking, tapping, and returning more often.
It differs from the Motivating-Uncertainty Effect because this one is about ongoing random rewards, while the other is about one single unknown prize that motivates effort.
Variable-Ratio Schedule Guide
Variable-Ratio ScheduleResearch
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.
The study showed how different reward schedules affected exercise in boys. The boys cycled and earned points for their performance, which they could trade for different rewards.
The findings showed that the Variable-Ratio Schedule rewards made boys cycle longer and more often.
Variable-Ratio Schedule Examples
1. Gambling
Casinos are the textbook example. Every element of slot machines, roulette, lotteries is a variable-ratio reward system. A slot machine might on average pay out 1 in 100 pulls, but the player doesn’t know when those 1 will occur - it could be on the 2nd pull, then not again for 180 pulls, etc. This uncertainty leads gamblers to sit for hours feeding the machine.
The act of refreshing your feed is reinforced variably – occasionally you see a post that really interests or rewards you (a friend tagged you, or a hilarious meme), which encourages you to keep scrolling. That’s why you can scroll indefinitely; the next scroll could surface something amazing. This has been explicitly likened to a slot machine by tech designers
Goal Gradient Effect Details
Goal Gradient Effect means we work harder as we get closer to the finish line. The smaller the gap, the stronger the motivation feels.
Think of a loyalty card that needs ten stamps. People speed up their visits once they see they’re close to completing it, even if they moved slowly at the start. Near the end, every step feels more rewarding.
In marketing this effect makes progress bars, milestones, and visible steps powerful. Showing people how close they are pushes them to finish the action, whether it’s a purchase, signup, or challenge.
Goal Gradient Effect Guide
Goal Gradient EffectResearch
A study showed that in a café “buy 10 get 1 free” programme, customers bought ~20% faster as they got closer to the reward, and when given a “12-stamp card with 2 free stamps” (endowed progress), they completed the card significantly faster even though the real effort was identical. After earning the reward, activity dipped, then restarted and sped up again as they approached the next goal.
A study found that when a fundraising campaign highlighted being 85% toward goal, donation rates more than doubled (from 0.5% to 1.17%), while showing 10% or 66% progress didn’t move behaviour. People act when they feel their contribution “finishes the job,” so motivation spikes only near the finish line.
Goal Gradient Effect Examples
1. Blinkist - reading streak & book completion bar
Blinkist shows a big progress bar for every book you read. When you reach 70-90% of a summary, you suddenly read faster to finish it. Users are more likely to complete books because the bar visually tells them they’re close to the goal. The more books you finish on the app, the higher the chance you'll go back to it.
Kickstarter campaigns speed up dramatically as the funding bar gets close to 100%.
At 70-90% funded, backers feel like the finish line is right there, so pledges jump fast.
Embargo shows customers exactly how many visits or points are left until they unlock their next reward. When diners see they are close to the goal, they visit more often and spend more, because the last steps feel faster and more exciting.
Temptation Bundling Details
Temptation Bundling means you pair something you should do with something you want to do, so the fun part pulls you through the boring part. The reward makes the task easier to stick with.
Think of only letting yourself watch your favorite show while exercising. The workout becomes less painful because the entertainment carries you through it.
In marketing this strategy makes habits stronger. Pairing valuable tasks with enjoyable perks, like learning with rewards or chores with small treats, keeps people engaged longer.
Temptation Bundling Guide
Temptation Bundling Research
Researchers led by Katherine Milkman tested if they can nudge people to go to the gym. They gave people fun audiobooks but locked them so they could only listen at the gym.
Afterward, 61% of participants said they’d pay to keep gym-only audiobook access, showing people actually want this kind of commitment device.
Temptation Bundling Examples
1. Amazon Kindle + audiobook “Whispersync”
Amazon links the “should” (reading) with the “fun thing” (audiobook). You only get the nice audiobook switch feature after you buy the ebook. People read more because the reward is tied to the action.
Play gives you reward points every time you top up or pay your phone bill. And those points can be swapped for Netflix, HBO, Disney+ and other streaming perks. So you do the “boring” task first (paying your bill), and you unlock the fun stuff after (free shows and movies). Classic temptation bundling.