Mr. Mischel begins by describing how, in the late 1960s, he and his colleagues devised a straightforward experiment to measure self-control at the Bing Nursery School at Stanford University. In its simplest form, children between the ages of 4 and 6 were given a choice between one marshmallow now or two marshmallows if they waited 15 minutes. Some kids ate the marshmallow right away, but most would engage in unintentionally hilarious attempts to overcome temptation.

They averted their gaze, covered their eyes, squirmed in their seats or sang to themselves. They made grimacing faces, tugged at their ponytails, picked up the marshmallow and pretended to take a bite. They sniffed it, pushed it away from them, covered it up. If paired with a partner, they engaged in dialogue about how they could work together to reach the goal of doubling their pleasure. (Type the text string “marshmallow test” in the YouTube search box to view the numerous videos.) About a third of the original subjects, the researchers reported, deferred gratification long enough to get the second treat.

I first learned of this research in a psychology graduate program in the 1970s, shortly after the original papers were published. At that time, the work was characterized as a study of “delay of gratification,” and there was not much fanfare surrounding the experiments. All that changed in 2006, when Mr. Mischel published a new paper in the prestigious journal Psychological Science. The researchers had done a follow-up study with the students they had tested 40 years before, examining the sort of adults they had grown into. They found that the children who were able to delay gratification had higher SAT scores entering college, higher grade-point averages at the end of college and made more money after college. Perhaps not surprisingly, they also tended to have a lower body-mass index.