Diet literally means "what you eat". It also means "what you don't eat", but usually for a short time to lose weight, after which you go back to your regular diet, i.e., "dieting".

This is where willpower comes into play. No willpower needed to eat. But once you start eating less - of total food or carbs or whatever - that's when you feel the effect of willpower. Willpower is used in the context of deprivation. Two things where it applies - hunger, and cravings. Hunger, that's easy: Eat. Cravings, that's another story. If you crave stuff you know makes you fat, you can't just eat that and still expect to lose fat if that's your original intent. But then, it's not just black and white, where you either eat or not eat. You can also eat that once in a while, then not eat that for a while. We'd call this a Carbohydrates Addict Diet, there's a book and everything, and a sub-forum right here.

Once we start to understand more about it, like the fact that hunger and cravings are not the same yet share physiological traits like dopamine (the hormone associated with learning and pleasure), we can then deal with those things more easily, more pragmatically. It allows us to think it through like we're doing here instead of just going about like zombies.