Agh. It's kind of mechanism our brain uses. As soon as we achieve something, we give us a little indulgence and sooner or later we break our goals.
For example, I managed to remove 9 kg since July (almost 20 pounds) and after that I ended breaking my diet and stopping the exercising when the anxiety went down a bit. The good thing is that I got used to a smaller food intake, so I have kept the weight. But tomorrow I'm back in the gym after almost one month of medical checkings. Although that means I will have to eat more, at 138 I can't go down much more without losing the ability to sit without a cushion.
My first habit to kill was this one: Untrain myself from what my mother engraved in my mind. Moms may be one of the main culprits of being fat (check Cracked for a good laugh). I was raised on "Clean the dish and lick it later, there are hungry kids in Africa and baby Jesus will cry". Etc Etc Etc. Every time I went out for lunch I would devour two dishes that were 150% of what I usually ate at home, with all the chips they always put and everything, because I was trained to think that If I did not do it I'd be insulting the cook. In the end I got used to read my stomach and stopping on time. Also, to ask the waiter to not put chips and replace them with salad.. think that now they are giving me smaller rations since I always leave half the dish empty.
The next one was... Fighting my mother again. She would stuff my work lunchbox with home biscuits, cakes, homemade muffins... When it has been four hours since you had breakfast and you still have three more until lunch, dieting is the last thing you think of. So every morning I would remove them and replace them with fruit.. The habit makes the monk, or so they say.
As Ronnie Coleman said, you can have a treat from time to time to kill the cravings.