The First 30 Days

What makes people stick with a New Year's resolution?

McClendon: Psychology is very simple—wherever you put your focus is what you're going to think, whatever you think is how you're going to feel, and however you feel is exactly what you're going to do. People need to write down their goal ("I will weigh this much," "My energy will be better," or "I will be able to do X"). By finding pictures in magazines that inspire you and by saying what you want out loud, you are reminding yourself of the way you want to be.

People fail because they forget this. When hunger starts and they see food that tempts them, their prior conditioning—the years of giving in to the wrong foods—will win out. But if people do a preemptive strike, so that every morning they look at what they really want, they will start to think differently.

What's the best way to make a New Year's resolution?

McClendon: Most of us are obsessed with the hows—the workout routine, the foods to eat or cut out, the time it's going to take to exercise. Why is a much more powerful motivator—to be a role model for my children, to have more energy to work and pursue my dreams, to feel good within my body, to be healthy and rested all the time, to finally feel I have what it takes to attract a partner, to support a friend for whom it's critical to overcome a health challenge. People accomplish more by answering the question "Why am I doing this?" than "How am I doing this?"