Your willpower is like a muscle, the more you use it, the weaker it gets. One reason to get up and exercise early is to habituate yourself to something that is good for you, without having to think about it. We are unconscious of most of the decisions we make throughout the day and by the time 5 o'clock rolls around we are exhausted and have a difficult time saying "I won't".
I have found this book to be invaluable in changing my behavior and making me aware of all the choices I make in a day so that I may become aware of the ones I'd like to change.
