An Incentive Too Far?
...Unfortunately, these assumptions that economists make about human motivation, though intuitive and straightforward, are false. In particular, the idea that adding motives always helps is false. There are circumstances in which adding an incentive competes with other motives and diminishes their impact. Psychologists have known this for more than 30 years.
In one experiment, nursery school children were given the opportunity to draw with special markers. After playing, some of the children were given “good player” awards and others were not. Some time later, the markers were reintroduced to the classroom. The researchers kept track of which children used the markers, and they collected the pictures that had been drawn. The youngsters given awards were less likely to draw at all, and drew worse pictures, than those who were not given the awards.
Why did this happen? Children draw because drawing is fun and because it leads to a result: a picture. The rewards of drawing are intrinsic to the activity itself. The “good player” award gives children another reason to draw: to earn a reward. And it matters — children want recognition. But the recognition undermines the fun, so that later, in the absence of a chance to earn an award, the children aren’t interested in drawing...
The Economist's Free Exchange is more sympathetic to the idea. Jared Bernstein was prompted to ponder a broader question: "Why Are Economists' Predictions So Often Wrong?" (in doing so, he takes a swipe at Mankiw, who responds).