Peak-End Rule

The rule comes from studies by Daniel Kahneman and his colleagues on how memory evaluates pain. In the cold-hand experiment, volunteers held a hand in painfully cold water for a short trial, and in another trial for the same time plus an extra stretch during which the water was warmed very slightly. Asked which trial to repeat, most chose the longer one: it held more pain in total but ended less badly. In a study with the physician Donald Redelmeier, patients undergoing a colonoscopy, then a painful procedure, rated their discomfort as it happened; their later memory of the whole procedure followed the worst moment and the final moments, while its length hardly mattered. A later study found that ending with a few extra minutes of milder discomfort left patients remembering the procedure as less unpleasant. Kahneman calls this indifference to length duration neglect, and in Thinking, Fast and Slow he uses these results to show that the remembering self, which makes our future choices, does not record experience faithfully. The rule cuts both ways. It can be used honestly, by ending a hard conversation, a treatment or a customer's visit well; and it deserves watching when we choose, because a strong ending can make the worse experience look like the better one.