The peak-end rule

Researchers had people hold a hand in painfully cold water and rate the discomfort in real time, moment by moment, and then again from memory afterward. The remembered rating was shaped by just two moments, the single worst point and how the trial ended, rather than by the average of the experience. In one version, they deliberately extended a trial by adding extra time at the end that was still uncomfortable but milder. Objectively that meant more total discomfort. Yet people remembered the longer version as less bad, because it ended more gently, and when offered the choice of which trial to repeat, most picked the longer one. Memory kept the peak and the ending, and threw the rest away.

What you keep of an experience is its most intense moment and its final moment rather than a fair average, and those two write the whole story afterward. This is why a candidate's single best answer and the handshake at the door can outweigh a flat hour in between, and why the last five minutes of a meeting can define how the whole thing felt. When you judge from memory, yours or anyone else's, know that the peak and the end are doing most of the talking, and the substance in the middle has dropped out of the memory.

Source: Kahneman, Fredrickson, Schreiber and Redelmeier, When more pain is preferred to less, Psychological Science, 1993. Kahneman tells the story in Thinking, Fast and Slow, 2011.

Thinking, Fast and Slow

Daniel Kahneman, 2011

The difference between the self that lives an experience and the self that remembers it.