The essence of emotional self-regulation is the ability to delay impulse in the service of a goal. The importance of this trait to success was shown in an experiment begun in the 1960s by psychologist Walter Mischel at a preschool on the Stanford University campus. Children were told that they could have a single treat, such as a marshmallow, right now. However, if they would wait while the experimenter ran an errand, they could have two marshmallows. Some preschoolers grabbed the marshmallow immediately, but others were able to wait what, for them, must have seemed an endless 20 minutes. To sustain themselves in their struggle, they covered their eyes so they wouldnt see the temptation, rested their heads on their arms, talked to themselves, sang, even tried to sleep. These plucky kids got the two-marshmallow reward. The interesting part of this experiment came in the follow-up. The children who as 4-year-olds had been able to wait for the two marshmallows were, as adolescents, still able to delay gratification in pursuing their goals. They were more socially competent and self-assertive, and better able to cope with lifes frustrations. In contrast, the kids who grabbed the one marshmallow were, as adolescents, more likely to be stubborn, indecisive, and stressed.