In a typical experiment, children are asked to solve problems that are rigged to ensure failure. After that, they’re asked to solve problems that are clearly within their capabilities. What happens? Even the latter problems now tend to paralyze them because a spiral of failure has been set into motion.
A kid who doesn’t do well assumes that if he does succeed, he must have just gotten lucky—or that the task was easy. And he assumes that if he fails again, which he regards as more likely, it’s because he doesn’t have what it takes: intelligence, athletic ability, musical talent, whatever.
Failure often leads kids to engage in something that psychologists call “self-handicapping”: They deliberately make less of an effort in order to create an excuse for not succeeding. This lets them preserve the idea that they have high aptitude. They’re able to tell themselves that if they had tried, they might have done much better.