In the 1970s, psychologist Walter Mischel conducted an experiment where he gave a group of children the choice to either eat a cookie immediately or wait until he returned and receive two cookies. The children who waited for the great reward were shown to do better in school go on to earn higher incomes. (Article source: https://www.psychologytoday.com/blog/happiness-in-world/201207/the-power-delaying-gratification)