As a verb, diet is defined as “restrict oneself to small amounts or special kinds of food in order to lose weight.”
So this is what people do. They want to lose weight (and they want to lose it NOW.) If they cannot adhere to this strict path they have put themselves on, they give up entirely.
Imagine starting a project on your house…. You lay out a timeline of when you want to complete certain aspects and you create a whole plan for yourself. Then something comes up. You get sick, you have to take so-and-so to the hospital, you’re working more hours than you imagined. Your timeline gets destroyed. Because you can’t put in the time you expected, you decide to stop working on it at all. In fact, you decide to tear the whole thing down and wait until you can execute your exact perfect plan.
I know this sounds ridiculous, but this is essentially what happens when you use the all or nothing approach. Your body and your health are a lifelong project. Things are going to come up, some days aren’t going to go according to plan, and sometimes you’re going to eat a cookie. That doesn’t mean you need to give up or wait until next week to start again. Balance means learning how to eat well most of the time and not spiral out of control if you eat something that isn’t ideal.