" You have one energy resource that is used for all kinds of acts for self-control. That includes not just resisting food temptations, but also controlling your thought processes, controlling your emotions, all forms of impulse control, and trying to perform well at your job or other tasks. Even more surprisingly, it is used for decision making, so when you make choices you are (temporarily) using up some of what you need for self-control. Hard thinking, like logical reasoning, also uses it.” Over the course of a day, dealing with traffic, frustrating bosses, and bickering children, plus—more insidiously—electronic temptations that are as alluring as fresh-baked chocolate chip cookies, a person’s supply of willpower is simply used up. "

― Laura Vanderkam , What the Most Successful People Do Before Breakfast: A Short Guide to Making Over Your Mornings--and Life