Why is it so hard to stick with a healthy eating or exercise plan? Why do we slip up or go back to our old ways? A lot of it has to do with the habits we've developed over time. We humans are creatures of habit. We tend to get settled into established, fixed ways of doing or thinking about things. Old habits can be hard to break. Because losing weight can mean changing quite a few habits at once, it can take more than just willpower to stick with a weight-loss plan.