Health behaviors—things like exercise, sleep, and diet—share in common a powerful impact on health by influencing obesity, cardiovascular disease, and most notably longevity. Unlike other “risk factors like age, gender, or family history, health behaviors are modifiable (you can change them), and therefore they provide a clear target for preventing certain diseases, both on a public and personal scale. We all know smoking is bad for us, that we should eat more salads and fewer cheeseburgers, and so on. But despite this knowledge, most people find it very difficult to change their habits, including the amount of physical exercise they get, over the long term, no matter how often they’re told to get up and get moving.