The Stanford marshmallow experiment was a series of studies on delayed gratification in the late 1960s and early 1970s led by psychologist Walter Mischel, then a professor at Stanford University. In these studies, a child was offered a choice between one small reward provided immediately or two small rewards if they waited for a short period, approximately 15 minutes, during which the tester left the room and then returned. (The reward was sometimes a marshmallow, but often a cookie or a pretzel.) In follow-up studies, the researchers found that children who were able to wait longer for the preferred...