IT BEGAN with some marshmallows. In the 1960s Walter Mischel, a psychologist then working at Stanford University, started a series of experiments on young children. A child was left alone for 15 minutes with a marshmallow or similar treat, with the promise that, if it remained uneaten at the end of this period, a second would be added. Some of the children, who were aged four or five at the time, succumbed to temptation before time was up. Others resisted, and held out for the reward.
Then, it was Dr Mischel’s turn to wait. He followed the children’s progress as they grew up. Those who had resisted, he found, did better at school than those who had given in. As adults they got better jobs, were less likely to use drugs and got into trouble with the law less frequently. Moreover, children’s family circumstances suggested that impulsive behaviour was as much learned as inherited. This suggested that it could be unlearned—improving the child in question’s chances in life.