Maria Konnikova, in The New Yorker, talks with Walter Mischel about his new book The Marshmallow Test: Mastering Self-Control:

Mischel believes that the skills which enable us to delay gratification are the same skills that allow us to make other good choices despite temptations to do otherwise. “We’ve found a way to really improve human choice and freedom,” he told me. “If we have the skills to allow us to make discriminations about when we do or don’t do something, when we do or don’t drink something, and when we do and when we don’t wait for something, we are no longer victims of our desires.” As Roy Baumeister, a professor of psychology at Florida State University who studies willpower, put it, self-control is like a muscle: the more you use it, the stronger it gets. Avoiding something tempting once will help you develop the ability to resist other temptations in the future.