This study is a (very) oldie, but an important goodie. And you’ve probably heard about it. In the late 1960s/early 1970s, Walter Mischel of Stanford University did a series of experiments with preschool children. The children were given a marshmallow (or a pretzel or a cookie). If they waited to eat the marshmallow for an unspecified amount of time (until the experimenter returned), the child would be given two marshmallows. At any point, the child could ring the bell on the table to have the experimenter return, but then they would only get the one marshmallow.