We talk a lot about willpower here at Lifehacker—why it's important, the science behind it, and how to boost it. Kelly McGonigal's career is dedicated to researching these things. As a psychologist and lecturer at Stanford, her work (and most recent book, The Willpower Instinct) focuses on self-control, motivation, procrastination, and how to overcome challenges to create healthier habits. When Kelly's not in the classroom (or on stage at TED), she's a founding member of the Yoga Service Council and group fitness instructor. We stole a few minutes of Kelly's very busy schedule (she did this interview via email on a plane!) to find out her best time-saving tricks, favorite playlists, and most inspiring advice.