I'm finding a lot of fascinating reading on behavioral economics-- the idea that people aren't rational economic actors, but instead behave economically just as irrationally as they do in other areas of life.
Consider this example from the Library of Economics and Liberty:
An example of suboptimal behavior involving two important behavioral concepts, loss aversion and mental accounting, is a mid-1990s study of New York City taxicab drivers (Camerer et al. 1997). These drivers pay a fixed fee to rent their cabs for twelve hours and then keep all their revenues. They must decide how long to drive each day. The profit-maximizing strategy is to work longer hours on good days—rainy days or days with a big convention in town—and to quit early on bad days. Suppose, however, that cabbies set a target earnings level for each day and treat shortfalls relative to that target as a loss. Then they will end up quitting early on good days and working longer on bad days. The authors of the study found that this is precisely what they do.