When it comes right down to it, we all know what we have to do to lose weight: Eat less, exercise more. And we also know what we have to do to get ourselves out of debt: Spend less, save more. The secret sauce that's the key to making these and other important life changes isn't really a secret at all. So why is it that we have so much trouble actually doing these seemingly simple things?

Because changing how we behave, particularly if we've been acting that way for many years, isn't easy. Our habits are often so ingrained that we don't even think about them on a day-to-day basis—until the number on the scale or the balance on our credit-card statement forces us to face the unsettling truth.

Here's the part where I tell you how to turn an unhappy situation around. Experts say that strengthening one area of your life (your finances, for example) can give you the confidence and fire you need to improve another part (like your waistline).

"When you get your act together in one way," says Michelle vanDellen, Ph.D., visiting professor of psychology at the University of Georgia, "you practice the behaviors necessary to pull your act together in others." You get better at resisting temptation, whatever it is—whether it's reaching for a double-fudge brownie or buying a pair of $600 heels—and the ability to resist becomes more habitual.