Yo-yo dieting is rampant. Why? "Because most trendy diets simply aren't sustainable over the long-term, so we jump on the bandwagon, follow the latest diet, but quickly feel deprived and fall off," Sheri says. Not many people are disciplined enough or willing to forego pasta and bread, wine, or treats for the rest of their lives — it's no way to live! When you follow the 80/20 rule, you give yourself permission to enjoy treats moderately. But you have to be able to revert back to healthful eating after each indulgence. It's not all or nothing; it's a lifestyle.