Here is an experiment you don’t want to try at home.

Show a toy  a doll, say, or a model boat  to a toddler and explain that it it’s something special you’ve had since you were little. Ask the child to be “very careful” with it. Hand over the toy, which appears to be in fine condition, except that you’ve secretly rigged it to break spectacularly as soon as the child handles it.

When your precious toy falls apart, express regret by mildly saying, “Oh, my.” Then sit still and observe the child.

The point is not to permanently traumatize anyone  the researchers who performed this experiment quickly followed it with a ritual absolving the child of blame. But first, for 60 seconds after the toy broke, the psychologists recorded every reaction as the toddlers squirmed, avoided the experimenter’s gaze, hunched their shoulders, hugged themselves and covered their faces with their hands.

It was part of a long-term study at the University of Iowa to isolate the effects of two distinct mechanisms that help children become considerate, conscientious adults. One mechanism, measured in other experiments testing toddlers’ ability to resist temptations, is called effortful self-control  how well you can think ahead and deliberately suppress impulsive behavior that hurts yourself and others.