While I’m not a fan of the term “diet”, your eating habits will determine upwards of 80% of your weight loss success. A successful “diet” is a lot like a successful relationship.
You have to be honest. If you’re not honest with yourself about EVERYTHING you eat, and aren’t honest about how MUCH you are eating, then you’re basically telling yourself “I’m just not that into you.”
You have to be faithful. No “cheating”. That said, if you pre-plan to build in “cheat” meals, then it’s not really cheating. It’s more like an open relationship that everyone agrees to. That said, if you’re not being HONEST (see above) about those planned indulgences, then it’s just plain cheating and it isn’t going to work out.
You have to be committed. This needs to be a long-term, lifestyle change. This isn’t just some two week fling. If you aren’t willing to stick with it, through the good times and the hard times, then you aren’t going to ever reap the benefits.