From losing weight to saving for retirement, willpower is the key to taking control of our lives. So says Kelly McGonigal, a health psychologist from Stanford University who’s just written “The Willpower Instict,” chronicling the science and practice of self control.

“Part of us kind of wants to want,” she tells Tess. “We go to the mall, or we’re searching online, and we like that feeling of wanting. It makes us feel optimistic.”

According to McGonigal’s “Terror Management Theory,” we feel more powerful when we buy status goods (handbags, cars, etc.) even if we can’t afford them. But, she says, paying attention to how spending makes us feel can give us a tool to managing our need for a short-term win that could really be a long-term loss.

Click on the audio player above to listen to the interview.