Deci tracked a bunch of college students who were solving puzzles for fun. He divided them into two groups. One group was allowed to keep solving puzzles as before. People in the other were offered a small financial reward for each puzzle they solved.

The psychologist later evaluated the volunteers: He found that people given a financial incentive were now less interested in solving puzzles on their own time. Although these people had earlier been just as eager as those in the other group, offering an external incentive seemed to kill their internal drive. …

Deci’s research into the counterproductive effects of threats and rewards has been replicated among high school students learning verbal skills, preschoolers trying to draw, and adults targeted by weight-loss, anti-smoking and traffic safety programs. In each case, external threats and rewards made it less likely that people would feel internally fired up about the goal.

So why are rewards and punishments employed so liberally?

“People like it because it is easy,” Deci said. “It is easy to offer a reward, but it is not easy to help people find their own motivation.”

⇒ When Play Becomes Work (via Mind Hacks.)