We have every evolutionary reason to want to keep score in life—passing on genes is a competitive business, after all. But there is no evidence that Mother Nature gives two hoots whether we are happy or not. And, in fact, this kind of scorekeeping is a happiness error for two reasons: It makes us dependent on external rewards, and it sets us up for dissatisfaction.

You can be motivated to do something intrinsically (it gives you satisfaction and enjoyment) or extrinsically (you are given a reward, such as money or recognition). Most people know that intrinsic rewards are the sweeter of the two. That’s basically what graduation speakers mean when they employ hoary nostrums such as “Find a job you love, and you will never work a day in your life.”

But there’s a twist: Psychologists have found that extrinsic rewards can actually extinguish intrinsic rewards, leading us to enjoy our activities less. In a classic 1973 study, researchers at Stanford and the University of Michigan showed this in an experiment with preschoolers. The researchers allowed a group of kids to choose their preferred play activities—for example, drawing with markers—which they happily did. The kids were later rewarded for that activity with a certificate featuring a gold seal and a ribbon. The researchers found that after they had been given the certificate, the children became only about half as likely to want to draw when they weren’t offered one. Over the following decades, many studies have shown the same pattern for a wide variety of activities, across many demographic groups.