As noted in chapter 2, most bad habits have a way of gradually growing back. As soon as you gain two pounds, immediately start watching your diet and exercise for the next few days until you lose the two pounds. After several months the desired behavior will become so routine that it will require little attention, except for a moment of attention occasionally to be sure you are still on target. More complicated contracts take more time. Later, it takes less time.
Habits are hard to predict, some changes are easy, some are unbelievably hard.
Common problems with the method Many people resist the idea of having their lives mechanically determined by rewards and punishment, even if they are entirely in control of rewarding the desired behavior. Some people just aren't organized enough to count and frequently reward a specific behavior. Nevertheless, the method works well, so if possible, give it a try. When required to make a self-improvement, reinforcement is the most common method used. I've seen thousands of such projects.