Seconded. There is a lot of noise on what diet is superior and which one works best. Intuitively a person knows when they've over indulged just as when we pull back when putting our hand in a flame. We just don't do it anymore, and design our lives around not ever having it happen again.
My only problem with this is the victim-hood that happens when this high carb crap clamours for our attention in ADs and the media. Invariably you will get victim-hood and people gorging and gulping their way to negate such imagery. I know I don't look at a McBigMac the same way when I've had one.
This also applies to healthy eating habits. Once you've reached your target weight and the novelty wears off, it's much harder to eat clean. Personally, I like pizza once per week, usually on Friday, as celebration and reward that it's finally weekend.
For exercise it boils down to discipline. At least for me. Plus, I feel really, really bad and get in a terrible mood if I cannot physically exert myself every day.