We only remember certain details of a whole experience; the peak and the end. Whether most parts of the experience were acceptable is without influence on the user’ss perception of the experience as a whole. An acceptable experience is often neither memorable, nor differentiating and will not be what makes or brakes your product.
Designing for the peak-end rule is about designing for the moments of truth. Moments of truth are where users experience how poor or good your product really is, and hopefully how it will help them kick ass. A sure moment of truth is at the end of an experience, but there are more. Find your product’s moments of truth through user research and address them. Emphasize them. Turn up the volume of the peak as much as possible and make sure it is pleasant so that it will leave a great lasting impression. Make sure that your peak and end is memorable, branded, satisfactory and different from your competitors.
An interesting twist to the peak-end rule was found when it came to measuring the experienced discomfort of pain. Consider the series 2-5-8 and 2-5-8-4 in which the numbers refer to reports of pain provided on a 10-point scale every 5 minutes. Rationally, adding 5 extra minutes of pain will only increase total discomfort, although experiments showed the longer period of pain (20 minutes), but with a period of diminished discomfort in the end, were rated less discomforting than the shorter period of pain (15 minutes), but with an increased discomfort in the end.
An episode, in which discomfort increases gradually to a high level, is evaluated similarly to an episode in which discomfort is high throughout. Furthermore, when test subjects were asked to evaluate moments, duration was completely neglected until they reminded themselves that it is better for episodes of discomfort to be short rather than long.
Designing for the peak-end rule is another way of not focusing on what is less important; about focusing on what brings the most value to the users’ experience.