You may think that a bad eating habit like overeating or eating foods that make you fat is harder to give up than most other bad habits because you can't simply stop eating altogether like a smoker can say, "This is my last cigarette."
Of course, quitting a habit like smoking isn't easy either. It's just different - but not really that different. There actually is a lot more to quitting any bad habit cold turkey than you might think. Even though it may seem on the surface that someone quit smoking "just like that", it isn't likely.
The smoker who quit cold turkey probably went through some important mental changes prior to taking such decisive action. Probably, she had to go from not even thinking of and wanting to quit, to thinking more and more about it, and preparing herself more and more mentally to give it up.
If you'd like to know more about the self-change process, try the book Changing For Good