It must be tough love week at Time magazine. First, there’s an interview with The Biggest Loser’s Jillian Michaels, who points out that if you want to lose weight, “I don’t mean just take the stairs. … I want half an hour, five times a week. ” You shouldn’t overdo it, of course, but that means “Don’t do more than eight hours a week,” Michaels says. Based on the interviews I’m doing for 168 Hours, 5 hours a week of exercise can get you in excellent (though not professional) condition. Of course, given how many exercise DVD offers I get promising results in 20 minutes per week, I think it’s safe to say that only 0.0001% of Americans are even risking overdoing it.

But that’s not what this blog post is supposed to be about.  I was most struck by an essay pointing out what should be obvious as Congress debates a credit card “Bill of Rights.” Yes, a lot of Americans are in credit card trouble in this economy, and no one likes the credit card companies. But people get in credit card debt the same way they become overweight: by failing to exercise discipline over their spending (or eating and exercising) . So Barbara Kiviat has a piece called “The Real Problem with Credit Cards: The Cardholders.” You can have all the disclosure you want, and you can regulate interest rates and fees. But it is just as possible to get into trouble at 19% interest as it is to get into trouble at 29% interest. Somehow, most Americans managed to get through life all right 40 years ago before consumer credit became widespread. Likewise, there are very few good reasons for building up debt now.

Debt, and obesity, both seem to be results of giving in to “hot emotions” — or at least that’s the phrase used by writer Jonah Lehrer in a recent issue of The New Yorker in a piece called “Don’t!: The Secret of Self-Control.” Lehrer writes about a long-term study following children studied at the Bing Nursery School near Stanford in the late 1960s. These 4-year-olds were put in a room with marshmallows. They were told that they could eat one now, or eat two in a few minutes when the researcher returned. Most of the children could not wait. But about a third could. It’s not that they didn’t want the marshmallow; they developed ways to distract themselves and so conquer their hot emotions. Decades later, these children grew into adults who did a much better job saving for retirement, controlling their weight, and even returning laptops to the researchers who tracked them down and asked them to complete some programs they’d installed on there.

This raises the nature-nurture question again. Are some people born more disciplined than others? Or can anyone learn these behaviors? Can a person who receives a Suze Orman smack down about her credit card debt learn to live within her means? Can an overweight person lose weight for good?

The answer seems to be yes — witness Jillian Michaels, who was overweight in her younger years. Her new book is called Master Your Metabolism, and while some of her scientific ideas are a bit odd (”remove all of the chemicals in your environment” — huh? Does she not understand that water, whole foods, air, etc. contain chemicals too?), the idea of daily self-mastery seems to be key. Tackling the idea of losing 50 lbs is overwhelming, but you can learn to say yes to healthier eating and exercise on any given day. I didn’t want to run 5 miles when I started this morning, but I did it anyway, and pretty soon I was enjoying it. Getting out of debt is also hard, but you can learn to say no to buying extraneous things and yes to saving on any given day.  Eventually, all these days add up, and self-discipline becomes a habit like any other.