Behavioral economics & viral marketing case studies
Placebo Effect 
Details
Placebo Effect means our expectations change how we experience a product or outcome. When we believe something will work better, it often feels like it does, even if nothing objectively changed.
Think of taking an expensive painkiller you believe is strong and feeling relief faster, despite it being identical to a cheaper one. The belief shapes the experience.
In marketing this bias shows up in branding, packaging, pricing, and framing. When something looks premium, advanced, or “scientifically proven,” people often experience better results because they expect them.
Goal Gradient Effect 
Guide
Placebo Effect
Research
In a 2005 study, participants drank the same energy drink, but some were told it cost full price ($1.89) while others were told it was discounted ($0.89).
After 10 minutes, they solved anagram puzzles. The full-price group solved about twice as many puzzles, while the discounted group performed ~50% worse, despite consuming an identical product.
Follow-up analyses showed this happened because a lower price reduced expectations, and those weaker expectations directly reduced performance.
In a separate experiment, people who drank a discounted energy drink reported greater fatigue and worse workout quality than those who believed they paid full price.
The authors concluded that pricing acts as a placebo (or nocebo) - discounts can literally make products work worse by lowering perceived effectiveness, even when the product itself does not change.
Placebo Effect 
Examples
1. Red Bull
People who believe they drank Red Bull perform better on tests and feel more alert.
The effect comes from expectation, not just caffeine. Branding and messaging amplify the perceived boost.
Painkillers labeled specifically for headaches are perceived as working better for head pain than general pain pills. Even when the formula is the same, the specific promise changes how strong the relief feels. The brain expects better results in that exact spot and often experiences them.
Because people believe Guinness must be poured “the right way,” they expect it to taste better after the ritual. This expectation changes the experience. Drinkers report smoother texture and better taste. The ritual doesn’t just pour the beer, it primes the brain to enjoy it more.
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.
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).
Law Of Proximity Details
Law of Proximity means we see things that are close together as belonging together. Our brains group nearby elements automatically, even if they’re not actually connected.
Think of looking at a row of icons on your screen. If two icons sit close to each other, you assume they’re related or part of the same category. Distance changes the meaning.
In marketing and design this law shapes how people read layouts, menus, and messages. Putting elements close together makes them feel linked, while spacing them out separates ideas and reduces confusion.
Law Of Proximity Guide
Law Of Proximity Research
A study showed that people who strongly react to the Law of Proximity in vision tasks are also more likely to show the attraction effect when choosing products.
In 2 experiments (100+ participants), people who grouped nearby shapes more strongly were also more likely to choose the option that sat “closest” to similar alternatives in a choice set, meaning proximity in layout makes one option feel naturally more attractive. This means product cards, pricing plans, or features placed close together can steer users toward the grouped option.
Law Of Proximity Examples
1. Trello
Trello keeps related things close together. Cards stay in one list, and lists stay together on a board. Because they sit side by side, your brain reads them as one unit. This makes the whole project feel easier to understand and manage.
HubSpot’s CRM uses proximity by keeping every key customer detail (notes, emails, deals, tasks) tightly grouped in one clean panel, so your brain instantly reads it as one story instead of scattered data.
Coca-Cola used the Law of Proximity to kill Crystal Pepsi. They launched Tab Clear, a cheap look-alike positioned as a diet soda, and placed it right next to Crystal Pepsi so shoppers would mentally link the two.
Because diet sodas were seen as weak and inferior, Crystal Pepsi instantly lost its “healthy mainstream” positioning, and the whole clear-cola idea collapsed.
Within 18 months, both products were dead, and Coca-Cola successfully destroyed the entire category with a deliberate sabotage strategy.
Tesler’s Law Details
Tesler’s Law means every feature should be as simple as it can possibly be. There’s always a minimum level of complexity in a system, and the goal is to cut it down until only the essential part remains. When you simplify past that point, things actually get harder to use. The system loses clarity, hides important steps, and forces users to guess.
Think of modern AI design tools that try to make everything one-click simple. They hide all the detailed controls, so you can’t fine-tune what you actually want. The tool feels easy at first, but the moment you need precision, you’re stuck fixing the image later in more complex software. The real work didn’t disappear, it only showed up somewhere else.
In marketing and product design Tesler’s Law pushes teams to find the sweet spot. Reduce friction, remove clutter, and make actions smooth, but keep the pieces that matter for understanding and control.
Tesler’s Law Guide
Tesler’s Law Research
The study challenged the idea that “simple design is always best.” The author showed that for powerful, feature-heavy software, too much simplicity actually makes the product weaker and less useful. The design should aim for “negotiated complexity” - simplify the parts that slow users down, but keep complexity where it adds value.
If your audience is advanced or your tool is professional-grade, some complexity is not a bug, it’s necessary power.
Tesler’s Law Examples
1. Gmail
Gmail offers a clean, minimal interface for reading and writing mail, while hiding a lot of underlying complexity (spam filters, threading, syncing, encryption, server protocols), so users don’t need to understand or manage all that complexity.
1. ChatGPT & Midjourney
AI image tools like ChatGPT or Midjourney are still too simple. You can’t precisely edit one part, so the model often changes the whole picture. Because of that, people still need advanced tools like Photoshop to fix the details.
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.
Familiarity Bias Details
Familiarity Bias means we trust and prefer things we already know. Familiar options feel safer, easier, and less risky than new ones, even if the new ones might be better.
Think of choosing a brand you’ve bought for years instead of trying a new one with better reviews. The comfort of the known beats the potential of the unknown.
In marketing this bias rewards consistency. Repeated exposure, steady branding, and showing up often make your product feel familiar, and familiarity drives choice.
In other words, we pick what feels known, not always what’s best.
Familiarity Bias Guide
Familiarity Bias Research
The study tested how being familiar with a brand, having previous online-shopping experience, and the amount of product information shown on a website, influence how risky people think online shopping is and whether they intend to buy.
The results:
Familiar brands and previous online shopping experience significantly reduced perceived risk and increased purchase intention. However, surprisingly, the amount of product information provided (lots vs little) did not significantly affect perceived risk or purchase intention.
Familiarity Bias Examples
1. Trello
Trello exploded because it took the Kanban board, a format millions already knew from offices, factories, and whiteboards, and turned it into super simple drag-and-drop software.
GPT-3 was powerful, but almost nobody used it because the interface felt technical and abstract. When OpenAI released ChatGPT with a simple chat-style UI, something everyone already knew from Messenger/WhatsApp, usage exploded within days.
Among Us blew up because its core gameplay was basically the digital version of Mafia/Werewolf/Secret Hitler - games millions already knew from parties.
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.
Decision Fatigue Details
Decision Fatigue means the more choices we make, the worse our decisions get. Our mental energy drains with every choice, and by the end we pick whatever is easiest, not whatever is best.
Think of grocery shopping at the end of a long day and grabbing random snacks at the checkout, you didn’t plan to buy. Your brain is tired, so it goes for the simplest option.
In marketing decision fatigue shows why fewer options, clear paths, and simple choices convert better. When people feel mentally tired, they choose the easiest button, plan, or don't buy at all.
Decision Fatigue Guide
Decision Fatigue Research
Researchers took a closer look at parole decisions made by experienced judges. It turned out that it was much more likely for the prisoner to be granted parole depending on the time of the day.
65% of positive decisions were made in the morning, when you're fresh, and fell dramatically later on. The rate returned to 65% after a lunch break and then fell again.
The jam experiment from 2000 proved that when there are too many choices we avoid making decisions to prevent making a bad one.
On the first day, people in a store were given 24 types of jam to choose from. On the second day, they were only given six. The group with fewer choices was 10 times more likely to buy something. This is because having lots of choices can make it hard to decide, so people choose not to decide at all.
Decision Fatigue Examples
1. Trader Joe’s
Trader Joe’s keeps things simple on purpose. Instead of giving you 20 types of ketchup, they give you maybe 2.
Flow State Details
Flow State means you’re so focused on a task that everything else fades away. Time moves fast, distractions disappear, and the work feels smooth and almost automatic.
Think of playing a game, drawing, or coding and suddenly realizing an hour passed without you noticing. You were fully inside the activity, not thinking about anything else.
In marketing and product design flow keeps people engaged for long periods of time. Clear goals, quick feedback, and tasks that are challenging but not overwhelming pull users deeper into the experience.
The right balance of focus and challenge makes the world fall away.
Flow State Guide
Flow State Research
A study with 400 online shoppers found that clean layout, nice visuals, small animations, and social presence all boosted the flow score to 4.10/5. One element (virtual atmospherics - the mood created by visuals, colors, animations, sounds, and micro-interactions) had a significant effect on flow. When the flow went up, purchase intention also went up significantly.
A study with 310 mobile-shopping users found that when an app is easy to use and clearly helpful, people enter flow. That flow then increases how much they like the app and how willing they are to buy.
Usefulness by itself didn’t change attitudes. It only worked through flow, meaning the full path was: useful + easy >> flow >> better attitude >> stronger purchase intention.
Flow showed a strong, meaningful effect on both attitude and buying, though the study didn’t report simple percentage changes. The core insight is that mobile shopping apps should feel effortless and genuinely helpful, because this creates flow, and flow is what makes people want to buy.
Flow State Examples
1. Duolingo
Duolingo keeps people in flow because every lesson is short, clear, and gets a bit harder each time. You always know what to do next. Instant feedback (green check, exp, streak, sounds) keeps your brain locked in. No big decisions, no friction. Users often do 10–30 minutes without noticing.
Sounds weird, but Trader Joe’s stores are engineered for flow. Small aisles, simple layouts, limited choices = no overload. Everything is clearly labeled and consistent, so shopping becomes automatic. Samples, colors, smells, and handwritten signs add micro-feedback and micro-discoveries. People get into a rhythm and finish shopping faster without feeling rushed.