Tell me if you can relate to this scenario. Today you commit to starting a diet. You say "I will be good. I will be good." You have a greek yogurt for breakfast. Lunch consists of a nice healthy salad. Then you go home...and proceed to eat the entire kitchen.
Yup, I can relate. Then I would say "I'll just start again tomorrow". Tomorrow turns to a week, turns to a month, winter brings spring...you get the idea. Then, you discover you've gained 20 pounds. It's a vicious cycle.