We judge an experience by its most intense point and its end, as opposed to the total sum or average of every moment of the experience. So tap into empathy, end on a high and make people feel great about using your service.
A 1993 study provided groundbreaking evidence for the Peak-End rule. Participants were subjected to two different versions of a single unpleasant experience. The first trial had subjects submerge a hand in 14°C water for 60 seconds. The second trial had subjects submerge the other hand in 14°C water for 60 seconds, but then keep their hand submerged for an additional 30 seconds, during which the temperature was raised to 15°C.
Subjects were then offered the option of which trial to repeat. Curiously, subjects were more willing to repeat the second trial, despite a prolonged exposure to uncomfortable temperatures. It was concluded that subjects chose the long trial simply because they liked the memory of it better than the alternative (or disliked it less).
When More Pain Is Preferred to Less: Adding a Better End PDF (Kahneman, Fredrickson, Schreiber & Redelmeier, 1993)
Designing emotional micro-interactions - The day of the Fuelband incident Blog post (ribot, 2013)