Your self-control “muscle” is just like the other muscles in your body; when it doesn’t get much exercise, it becomes weaker over time. But when you give it regular workouts by putting it to good use, it will grow stronger and stronger, and better able to help you successfully reach your goals.

To build willpower, take on a challenge that requires you to do something you’d honestly rather not do. Give up high-fat snacks, do a hundred sit-ups a day, stand up straight when you catch yourself slouching, try to learn a new skill. When you find yourself wanting to give in, give up, or just not bother—don’t. Start with just one activity and make a plan for how you will deal with troubles when they occur (“If I have a craving for a snack, I will eat one piece of fresh or three pieces of dried fruit”). It will be hard in the beginning, but it will get easier, and that’s the whole point. As your strength grows, you can take on more challenges and step up your self-control workout.

Many of the goals we struggle with year after year have one thing in common: resisting temptation. Trying to ignore the powerful allure of the forbidden cigarette, doughnut, or latest budget-blowing buying impulse requires willpower. When faced with a boring expense report or a dense white paper, it takes self-control to avoid checking Facebook, answering e-mail, or firing up a game of solitaire. And for some, it takes even more strength of will to keep their temper in check at work when a colleague “just doesn’t get it” or a subordinate makes a mistake.

You might expect very successful people, who presumably have boatloads of willpower, to be particularly good at not giving in. But if anything, they seem to be even more susceptible to temptation than the rest of us. Quick—name a famous or powerful person who doesn’t have a well-known weakness for something. I’ll wait.

Having the willpower to govern a country, yet lacking the willpower to resist cigarettes or french fries may seem like a contradiction, but it actually isn’t, according to research on the nature of self-control. To understand why, you need to understand how willpower really works.

Your capacity for self-control is not unlike the muscles in your body. Like biceps or triceps, willpower can vary in its strength, not only from person to person, but from moment to moment. Just as well-developed biceps sometimes get tired and jellylike after a strenuous workout, so too does your willpower “muscle.”

Even everyday actions like decision making or trying to make a good impression can sap this valuable resource, as can coping with the stresses of your career and family. When you tax it too much at once, or for too long, the well of self-control runs dry. It is in these moments that the doughnut wins.

The good news is that willpower depletion is only temporary. Give your muscle time to bounce back, and you’ll be back in fighting form and ready to say no to any doughnuts that come your way. Recent research shows that when rest is not an option, you can actually speed up your self-control recovery or give it a boost when reserves are low, simply by thinking about people you know who have a lot of self-control. (Thinking about my impossibly self-possessed mother does wonders for me when I’m tempted to snap at someone.)

Or, you can try giving yourself a pick-me-up. I don’t mean a cocktail; I mean something that puts you in a good mood. (Again, not a cocktail—it may be mood enhancing, but alcohol is definitely not willpower enhancing.) Anything that lifts your spirits—listening to a favorite song, watching a funny video, calling a good friend, or reflecting on a past success—should also help restore your self-control strength when you’re looking for a quick fix.

The other way in which willpower is like a muscle (and the really great news for those of us struggling to get our impulses under control) is that it can be made stronger over time, if you give it regular workouts. Recent studies show that daily activities such as exercising, keeping track of your finances or what you are eating—or even just remembering to sit up straight every time you think of it—can strengthen your capacity for self-control. For example, in one study, people who were given free gym memberships and stuck to a daily exercise program for two months not only got physically healthier, but also smoked fewer cigarettes, drank less alcohol, and ate less junk food. They were better able to control their tempers and less likely to spend money impulsively. They didn’t leave their dishes in the sink, didn’t put things off until later, and missed fewer appointments. In fact, every aspect of their lives that required the use of willpower improved dramatically.

So if you want to build more willpower, start by picking an activity (or avoiding one) that fits with your life and your goals—anything that requires you to override an impulse or desire again and again—and add this activity to your daily routine. Examples from past research include giving up a favorite sweet, refraining from cursing, using your nondominant hand to open doors and brush your teeth, and avoiding starting sentences with “I.” But you can choose just about anything for your self-control exercise, so long as it involves overcoming an urge—doing something you’d rather not do. Depending on your habits, making your bed each morning or limiting your time on Facebook might be a good place to start. It will be hard in the beginning, but it will get easier over time if you hang in there, because your capacity for self-control will grow.

Putting It into Practice: Pump Up Your Self-Control Muscle

1. Willpower gets depleted with use. When the tank is empty, give yourself a rest before tackling a new self-control challenge.
2. You can speed up your recovery by doing something to lift your spirits, rewarding yourself for good behavior, or by just thinking about someone you know with lots of self-control.
3. Your willpower muscle will grow with regular exercise. Before taking on a goal that requires lots of willpower (e.g., quitting smoking, radically changing your diet), start by strengthening your muscle with regular, less strenuous workouts. Add a few willpower challenges to your day (e.g., making your bed, sitting up straight, taking the stairs instead of the elevator) and build from there.