Roy Baumeister In TIME: Willpower Isn't Unlimited—So Use It Wisely
Willpower is, in a sense, finite. "After making a lot of decisions, your self-control is lower and conversely, after exerting self control, your capacity for making decisions is lower," he explains. "As you make a bunch of decisions, you gradually deplete the energy you have available and subsequent decisions are more passive and tend to go with the default option." Because you can eventually deplete your ability to think things through, you are likely to make poor decisions and not exercise good self-control. He gives the example of someone buying a car to explain his point. After having to choose between hundreds of options for seat fabric and car color, the person eventually becomes exhausted and will passively say yes to other expensive options they wouldn't purchase otherwise.
However, he says that knowing that your willpower is a finite resource can help you conserve and improve it. He suggests saving big decisions for early in the week if possible—not on a Friday when you are worn-out. Also, he says having routines can help conserve willpower. If you have set patterns you follow each morning you won't be expending copious amounts of energy deciding what to eat for breakfast. Rest, sleep, and exercise are also good tools for keeping your reserve of self-control in tip-top shape. In his numerous publications and keynotes, the highly regarded psychologist expands on the points he discusses in the article, and in Willpower. He is a highly requested speaker on personal motivation and explains that self-control is perhaps the most important component of success.