Each chapter of the book revolves around a central argument: Habits can be changed, if we understand how they work. It focuses on habits as they are technically defined: the choices that all of us deliberately make at some point, and then stop thinking about but continue doing, often every day. Habits is a formula our brain automatically follows: when I see CUE, I will do ROUTINE in order to get REWARD. To re-engineer that formula, we need to begin making choices again. And the easiest way to do this, according to many studies, is to have a plan to trick the brain from sending us on an unwanted path.
A summary of the book can be read here.