Emphasizing momentary failures hinders long-term weight-loss success.

"The biggest myth about willpower," says Barbara Rolls, acclaimed professor of nutritional sciences at Penn State and author of The Ultimate Volumetrics Diet, "is that it's always going to be there." Self-control with food eludes everyone eventually. If you keep your eye on the long-term goal--new habits, overall behavorial changes-- a short-term setback loses its symbolic power. "We all have moments of weakness, but if you find that motivation, it's going to be easier. But it's not easy," Rolls says.

The side effect of putting too much stock in the idea of willpower (4 o'clock doughnut equals catastrophic failure) is what obesity researchers call the "What the Hell?" effect: As soon as you eat something you think you shouldn't have, you figure you've lost the battle for the day and might as well eat what you want. Instead, do some calorie compensation at the next meal. Your daily intake will probably still be fine, and you'll feel like a success.

Motivation needs to be front of mind, and for that it helps to have buddies. One member of Cooking Light's Social Diet group, Allison Lowery, has beat the What the Hell? effect thanks to the team dynamic. "I see others not throwing in the towel, so I feel a responsibility to keep at it," she says. Regardless of where your motivation comes from, losing weight can't be your sole motivator. "It should be honestly getting to the point where you enjoy healthy eating patterns and realize you can't eat everything all the time and you don't need to," Rolls says. "If you have healthy defaults in place, then it won't matter as much if your willpower fails."

When willpower does falter, Lowery has a rule: Be kinder to yourself. "Beating yourself up isn't going to motivate you. I keep my fun foods, make portions more reasonable and stay motivated on the fitness front."