Peak-End Rule
We judge an experience primarily by how we felt at its most intense point and at its end.
The peak-end rule is a psychological heuristic in which people judge an experience based on how they felt at its peak (most intense point) and at its end, rather than based on the sum or average of every moment of the experience. It was developed by psychologist Daniel Kahneman. The rule explains why a medical procedure that ended well is remembered better than an objectively less painful one that ended unpleasantly.
What it looks like in the wild.
- Everyday life Cold Water Experiment Kahneman's experiment: people preferred immersing a hand in painfully cold water for 90 seconds if the last 30 seconds were slightly warmer, over 60 seconds of the same cold water.
- Marketing Last Impression Design Product unboxing experiences are meticulously designed to end on a high note because that peak and ending form the remembered experience.
Someone has already built a business on this.
Biases are not only private errors. They are design targets — patterns deliberately engineered into interfaces because they reliably work.
- E-commerce High-End Checkout Experience E-commerce platforms invest in luxurious confirmation pages and emails because the ending of the purchase experience disproportionately shapes the remembered satisfaction.
Recognising a definition is not the same skill as spotting it.
Two scenarios from the app, with distractors drawn from the same family of biases — which is what makes them hard.
Tom hated his job, but on his last day, his boss gave him a heartfelt goodbye card. He quit feeling the overall experience was positive.
A person enjoys a boring but challenging puzzle because the final piece fitting into place felt incredibly rewarding.
Biases rarely arrive alone.
Understand more. Assume less.
188 biases, 18,869 scenarios, and a record of how you actually decide.
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