Peak-end Rule

According to the peak-end rule, we judge our past experiences almost entirely on how they were at their peak (pleasant or unpleasant) and how they ended. Other information is not lost, but it is not used. This includes net pleasantness or unpleasantness and how long the experience lasted.

In one experiment, one group of people were subjected to loud, painful noises. In a second group, subjects were exposed to the same loud, painful noises as the first group, after which were appended somewhat less painful noises. This second group rated the experience of listening to the noises as much less unpleasant than the first group, despite having been subjected to more discomfort than the first group, as they experienced the same initial duration, and then an extended duration of reduced unpleasantness.

This heuristic was first suggested by Daniel Kahneman and others. He argues that because people seem to perceive not the sum of an experience but its average, it may be an instance of the representativeness heuristic.