Portion control! I think many people think that a diet needs to consist of depriving yourself of the foods that you love. This is a myth. It is all about watching how much you eat, not as much about what you eat.
Many people do not realize what the actual serving size is for the foods. If you want to eat a piece of chocolate, that is fine. As long as it is a piece, not the entire candy bar.
When you deprive yourself of the foods you love, I think this will make you want to stop your diet completely. There are ways to make foods you love low-calorie, low-fat. You could substitute ingredients.