After hundreds of experiments to discover what the best prediction is for future success, the Stanford psychologist Walter Mischel found that a simple experiment with a marshmallow was the best predictor.
The experiment runs as follows. A young child is seated in a room on a chair. In front of him or her is a table with a plate with one marshmallow on it.
Then the child is told that he is allowed to eat it, if he wants.
But if he waits until the supervisor comes back, he will get another one, so he will have two!
The child is then left unattended for about 15 minutes, while his behaviour is recorded.