IN THE 1960s, Walter Mischel at Stanford University carried out an experiment to test the effects of delayed gratification in children. The subjects of his study were a random sample of 4-year-old children. The children were led into a plain room, one-by-one, where Mischel presented each with a marshmallow on a plate. Children were told that they were free to eat the marshmallow, but any child who waited to eat the marshmallow until Mischel returned from an errand, would receive two marshmallows.

Some of the children immediately crammed the marshmallow into their mouth with Augustus Gloop–like voracity as soon as the researcher left the room. Others were able to wait for a few moments, but then succumbed to the overpowering temptation of the marshmallow. Another group of children engaged in a variety of self-distraction exercises: covering their eyes so they could not see the marshmallow, walking over to sit in a corner, singing, and playing clapping games with themselves. When Mischel returned, he rewarded these children with their second marshmallow. Then he waited for the children to grow up.

What he found fourteen years later was astonishing. The children who had waited for the second marshmallow scored an average of 210 points higher on the SAT than those who couldn't wait.