In 1996, psychologist Roy Baumeister, Ph.D. conducted a cruel experiment. With some of his former Case Western Reserve University colleagues, he studied the effect of tempting participants with scrumptious treats in order to see how much willpower human beings actually have.
He kept the 67 participants in a room that smelled like freshly baked chocolate cookies, then showed them the cookies and other chocolate bonbons. Some got to indulge, and others were asked to eat radishes instead. After this torture, the team assigned the participants a difficult geometric puzzle. As you might imagine, the folks who got stuck eating the radishes did far worse on the puzzle than the ones who got to indulge in the treats.
Two years later, Baumeister published the study in the Journal of Personality and Social Psychology and the concept was born that our willpower is finite. The unlucky peeps who were forced to eat veggies simply no longer had the will to engage in another task that tapped their resolve. They were too tired and probably ticked off to work on any puzzle.