Whether we have lived a pleasant or unpleasant experience, we often only remember the most intense parts as well as the ending rather than some type of average of all our emotions. This is due to the peak-end rule, a concept first presented by Daniel Kahneman which has many applications our everyday lives. The reasons behind this phenomenon are the fact that people have a better recollection of moments that are intensely emotional and the recency bias, the fact we remember the end of an event better than the rest. This rule is particularly used in the field of medicine to make medical procedures less painful but also in fields such as business and management (for consumer interactions, leading and motivating teams, etc.)
A study was conducted in 1993 where participants had to submerge their hand in 14° water for a minute. They then had to repeat the experiment but in the second round, an extra 30 seconds was added to the initial minute where the temperature was raised by one degree. Participants were more willing to repeat the second round of the experiment than the first, despite the prolonged exposure to the pain.