Self control is huge, for me.
I heard a statement on a documentary about health, obesity, pharma companies and drugs, and how we eat that REALLY shined a light on my constant excuse-making in regards to how I eat at times.
Paraphrased: For most people who complain that they can't control their eating habits it boils down to their philosophy on eating. To say "I can't have it but I want to" is an extremely weak statement when compared to "I can't have it, but I don't want to".
They then went into why most people fail on a diet, but basically because they are trying to completely restrict a food group or food in general. Then when the diet is "done" they go back to eating normally and gain it all back. One of the nutritionists they interviewed stated that the term diet isn't about how we restrict ourselves like most people view a "diet" but about what we actively eat to maintain a proper homeostasis in our bodies and energize us. Very interesting documentary, very thought provoking, but I liked the can't/want quote, that really struck a chord with me.