It seems that our memory is not entirely reliable when it comes to remembering whether a particular experience was good or bad. According to Barry Schwartz’s book The Paradox of Choice, the quality of our memories of an event are determined by two things.
One thing is the most intense emotion you felt during the experience (whether good or bad). The other thing is how good or bad the experience felt when it ended. The last part is the fascinating one, and indicates that memories can be manipulated.
Schwartz tells of a specific experiment where doctors perform a so-called diagnostic colonoscopy on a number of male patients. This is medical speak for a pretty unpleasant exercise involving your rectum and a moving tube with a small camera attached. As you may imagine, patients habitually report the experience as highly unpleasant (I guess that it is not the favorite passtime of the doctors, either).
Interestingly, the researchers varied the setup: after performing the examination, the doctor left the tube in place for a little while. This was still unpleasant, but much less so since the doctor was not moving it around. Although this made the whole experience longer, the patients experienced the procedure as less unpleasant because of the relatively more pleasant ending.
Conclusion: If you want to influence people’s memory of events, work on making the last part more pleasant.