Just imagine you're four years old, and someone makes the following proposal: If you'll wait until after he runs an errand, you can have two marshmallows for a treat. If you can't wait until then, you can have only one--but you can have it right now. It is a challenge sure to try the soul of any four-year-old, a microcosm of the eternal battle between impulse and restraint, id and ego, desire and self-control, gratification and delay... There is perhaps no psychological skill more fundamental than resisting impulse. It is the root of all emotional self-control, since all emotions, by their very nature, led to one or another impulse to act.