Behavioral economics & viral marketing case studies
Law of Similarity 
Details
Law of Similarity means our brain naturally groups things that look alike. When objects share color, shape, size, or style, we treat them as belonging together, even if they aren’t.
Think of seeing a shelf full of products where a few items use the same bright color. Your eyes automatically pair them and assume they’re part of a set or the same brand, even before reading any label.
In marketing this bias shapes how brands design packaging, product lines, and website elements. When similar things look unified, people find them easier to understand and navigate.
Law of Similarity 
Guide
Law of Similarity 
Research
The study tested whether the Law of Similarity can make our visual working memory (VWM) work better. Earlier research shows that VWM usually stores only about 4 items, so the question was, can similarity help us hold more?
Overall, the research shows that the Law of Similarity helps memory by letting the brain “chunk” similar items into one group, but this only works when the items are visually close to each other. If they are too far apart, the brain does not group them, and the benefit is lost.
Law of Similarity 
Examples
1. Supermarket packaging copies
Many private-label brands intentionally design their packaging to look almost identical to the leading brand - same color layout, same typography rhythm, same imagery. Shoppers think “looks like the one I know so it must be good.” These lookalike designs often boost sales massively because:
Coca-Cola used the Law of Similarity 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.
Affect Heuristic Details
Affect Heuristic means we make decisions based on our immediate feelings instead of careful thinking.
How we feel shapes how we see risk and reward. When people feel good they are more likely to take risks and focus on potential great rewards. But when their mood turns dark they may become more risk-averse and focus on potential losses. This swing of emotions can tip the scales in how choices are made.
Think of choosing a product simply because it gives you a good vibe, even if you didn’t compare features or prices. The feeling made the choice for you.
In marketing this heuristic shows why mood, colors, music, faces, and tone matter. Positive feelings make risks seem smaller and benefits seem bigger.
Affect Heuristic Guide
Affect HeuristicResearch
95% of our purchasing decisions are emotional. Most of our buying decisions come from the subconscious. We think we’re comparing features and prices, but in reality we react to emotions, associations and mental shortcuts we don’t notice.
After looking at 1,400 ad campaigns from the last 30 years, the study showed that ads focused just on emotions almost doubled the success rate (31% profit boost) compared to those that stuck to facts and logic (16% boost).
One field study showed that hungry shoppers spent 64% more money and grabbed more items even non-food ones.
In a lab test, hungry students took 50% more binder clips than students who had eaten. They didn’t suddenly “love” binder clips. Hunger just created a general urge to grab more stuff. Hunger boosts the desire to consume anything, not just food.
Retailers like Trader Joe’s or Home Depot offer free coffee to their customers. And if you drink coffee before you shop, you’re likely to buy 30% more items and spend roughly 50% more money.
Works for the feel-good products - scented candles, fragrances, home decor. Not so much for practical things like notebooks or kitchen utensils.
Affect Heuristic Examples
1. Starbucks
Starbucks doesn’t just sell coffee. It sells warm lighting, cozy music, and the smell of fresh beans. This positive emotional atmosphere creates a comfort halo. Because customers feel good in the space, they perceive the coffee as higher quality and the price as more reasonable, even though logically it’s much more expensive than competitors. The pleasant vibe lowers the perceived risk of overpaying.
Tesla owners often report extremely positive feelings toward Elon Musk and the brand. That emotional attachment makes many buyers gloss over objective risks like build-quality issues, recalls, or long repair times.
The cool, futuristic, mission-driven vibe creates positive affect, which leads to quick, intuitive decisions like Tesla = innovative = safe/best choice, even when data doesn’t fully support it.
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.
Unit Biasy Details
Unit Bias means we feel the urge to finish a full unit of something, no matter its size. If it’s presented as one piece, one portion, or one task, our brain treats it as the natural amount to complete.
Think of eating a whole chocolate bar even when you’re not that hungry, just because it comes as one bar. If it were split into tiny pieces, you’d likely stop earlier.
In marketing this bias shapes how people consume and buy. Portion sizes, product bundles, and task steps guide behavior simply by defining what “one” looks like.
Unit Bias Guide
Unit BiasResearch
A key study by Geier, Rozin, and Doros (2006) introduced the term “unit bias.”. In the pretzel test, one group got a whole pretzel and another group got half. Those who got a whole pretzel ate the whole thing, even though it was twice as much food.
Those who got only half felt it was also enough size, because their brain treated that half as a full unit.
In a study, when people got 4 small 100-calorie snack packs, they ate about 25% fewer calories than those who got the same food in one big 400-calorie bag. They could open all four packs, but most stopped after one, because one pack felt like “one serving.”
Unit Bias Examples
1. Coca-Cola’s mini cans
By selling soda in smaller cans (90 calories vs 140+ in a standard can), Coke charges a premium per ounce, but consumers don’t mind because one can feels like a full serving.
TikTok was the first big app to use unit bias with infinite scroll for short videos. With normal pagination, one page feels like one “unit,” so people naturally stop after finishing it. TikTok removed that stopping point. Each video feels like one tiny unit, and the app instantly gives you the next one with no break. Your brain never gets a “time to stop” signal, so you keep watching longer than you planned.
Sensory Appeal Details
Sensory Appeal means we pay more attention to things that wake up our senses. When something looks better, sounds clearer, feels smoother, or smells richer, it becomes more memorable and more tempting.
Think of walking past a bakery and catching the smell of fresh bread. You weren’t hungry a minute ago, but that scent pulls you in faster than any ad ever could.
In marketing sensory cues make products feel more real and more desirable.
Sensory Appeal Guide
Sensory AppealResearch
Researchers tested how scent changes buying behavior by putting identical Nike shoes in two rooms. One smelled like flowers, one had no scent.
People were 84% more likely to choose the scented-room shoes. This study helped spark today’s $200M scent-marketing industry.
The 2019 Mood Media study showed that turning on music, screens, and scent in an INTERSPORT store boosted sales by 10%. Shoppers also stayed longer 13.4 minutes vs. 7.9 minutes with everything turned off.
Adding scent in the “Football Zone” raised positive feelings by 28% and increased sales by 26%. Letting people touch products lifted emotional response by 50%, and 56% of shoppers said touch is the biggest reason they buy in-store.
Holding an item makes people up to 48% more likely to choose it or choose another product with the same shape/size.
People were 48% more likely to pick a chocolate when its shape matched the object they were already holding.
People were 39.9% more likely to choose a Fanta when they were holding a can or a bottle shaped like it.
The effect became up to 208% stronger when products were packed tightly together on crowded shelves, because touch helped people process them faster.
BIT (Behavioral Insights Team) wanted to influence meat-eaters to choose vegetarian food instead.
They only added a few words, such as:
Results? Sales of vegetarian options increased by up to 70%!
Sensory Appeal Examples
1. Starbucks
Starbucks is famous for its in-store aroma – they intentionally grind coffee throughout the day because the rich coffee smell entices people inside and makes the experience cozy.
Singapore Airlines even made its own cabin scent “Stefan Floridian Waters” so passengers instantly feel “this is Singapore Airlines.”
Observer Expectancy Effect Details
Observer Expectancy Effect means people change their behavior when they sense what someone else expects from them.
Think of a teacher who quietly believes certain students will do better. Those students often perform higher because they pick up on tone, attention, and small signals, even if no one says anything out loud.
In marketing this effect shows up in testing, interviews, and research. When customers sense what you want to hear, their answers shift and the data gets distorted.
In other words, people try to match the expectations they feel around them.
Observer Expectancy Effect Guide
Observer Expectancy EffectResearch
A British university coffee lounge hung an image of a pair of eyes on contributions to an honesty box that collected money for drinks.
The image of eyes primed people to pay nearly 3 times more for their drinks than they would have without the image.
A real-world cafeteria experiment showed that when posters had eyes on them, more people cleaned up their own mess compared to normal posters.
Even in places where cleaning up after yourself is expected, people do it more when they feel like someone might be watching, even if it is just a picture of eyes.
Observer Expectancy Effect Examples
1. Github
GitHub’s public grid of green squares shows how often you commit code. Because everyone can see your activity (teammates, recruiters, other devs) people commit more often to avoid empty streaks.
Nobody is actually watching, but the possibility that someone might see your activity pushes more consistent behavior.
Signs like beware of the dog or this area is monitored make people behave better or avoid trouble, even when nothing is actually watching them.
The hint of possible observation or risk is enough to change behavior (fewer trespasses, less littering, less vandalism) all triggered by the feeling that someone (or something) might see them.