Peak–end rule
We judge a past experience by its most intense moment and how it ended, not by its sum.
What it means
The peak–end rule is the finding that retrospective evaluations of an experience are dominated by how it felt at its emotional peak and at its end, rather than by the total or average of every moment that made it up. The mechanism reflects the gap between the 'experiencing self,' which lives through each moment in real time, and the 'remembering self,' which constructs a summary judgment from a few salient snapshots — chiefly the most extreme point and the final point — and largely ignores how long the experience lasted (duration neglect). This produces choices that systematically favor remembered well-being over experienced well-being, sometimes perversely, as when people prefer an objectively longer episode of discomfort because it ended more gently. The classic colonoscopy studies demonstrated that adding a stretch of milder discomfort at the end made the whole ordeal be remembered as less unpleasant, even though more total pain was endured. It matters because the remembering self is what decides whether to repeat experiences, so designing the peak and the ending of services, products, and care can shape memory and future choice more than improving the average moment.
Examples
A longer colonoscopy with a gentler ending was remembered as less unpleasant than a shorter, sharply painful one — more total pain, but a kinder finish.
A rainy week away is remembered fondly for one perfect afternoon and a lovely last dinner; the four grey days in between barely register in the retelling.
A theme park's fireworks finale and an easy walk back to the car do more for how the day is remembered than shaving ten minutes off every queue.
First described in Kahneman, Fredrickson, Schreiber & Redelmeier (1993).