From Boom and Gloom:
...the Peak/End rule. When people assess a past experience, they pay attention above all to two things: how it felt at the peak and whether it got better or worse at the end. A mild improvement - even if it's an improvement from "intolerable" to "pretty bad" - makes the whole experience seem better, and a bad ending makes everything seem worse...
...people are on what's sometimes called a "hedonic treadmill," meaning that as they get wealthier they quickly adapt to their new circumstances. At first, you love your Lexus, but before long it may as well be your old Pinto. But if you lose the Lexus you don't easily get over it. "Loss makes you more unhappy than gain makes you happy," Krueger says.