3. Bad chemistry
Willpower requires actual energy—specifically, glucose. Several studies have shown that when we use willpower, we eat away at our stores of glucose. If we fail to replenish these stores, then our ability to muster our resolve stays low. On the flip side, a shot of glucose—say, a few sips of real juice or a piece of fruit—can fill those reserves back up. The key is, it must be actual sugar: Florida State University psychologist Roy Baumeister showed that subjects who drank lemonade sweetened with a sugar substitute were not able to restore their self-discipline to the same degree as those drinking lemonade that contained real sugar.
Translation: Before you give up on your goal for the day, try to have something sweet—a piece of fruit is obviously better than a sugary drink or treat, but if that’s all you have on hand, limit your portion to a few sips or small bites.