I have blamed a lot of people's diet failures, including myself, on lack of willpower.
As we know, there are just some delicious, sweet, salty, fatty, and processed foods we can't seem to escape.
But as this article, Eating too much? You can blame your brain , explains; willpower may not be the primary culprit in falling victim to cravings.
If you have 10 minutes to browse through this, I think you'll find interesting the science behind any cravings and overeating problems (especially junk) you may have.
If you don't have time to read the entire article, jump to the Change what you eat, change your brain section. This will reinforce many of the habits you can use to change your chemistry to improve your health, body composition, and performance.