But that's just it, your willpower may run out, as it's a finite resource, and what will you do then?
Accept the temporary setback, don't let it demolish your resolve and try again. While willpower is not infinite, you can increase your reserves. It's another kind of habit, I suppose. I do speak from experience.
It is also necessary to change your relationship to food. I don't do without chocolate or carbohydrates, but I've learned to find a small portion of them, among more healthy food, rewarding. And I relearned how to like the healthier food for itself. I changed the proportion of protein, carbs and vegetables on the plate, stopped having desert with every meal. I made it easier not to cheat by eating the green veg first and the chips last, so that if I was beginning to feel full, it would be the more calorific things that might be left. If I'm eating out, I usually exercise some restraint (salad or green veg rather than potatoes, new potatoes rather than chips, maybe constructing a meal from two or three starters rather than a starter and a large main course) while also allowing myself a small treat. And sometimes I do just have an indulgent meal - although my concept of what is indulgent has changed a bit. Getting back to cooking for myself properly was a *big* part of all of this.
All of that made it easier, but I still had to eat less and endure some discomfort while my body adjusted. I didn't manage it all at once, but I never let myself take as many steps back as I had taken forwards, so even when I did relapse it wasn't devastating to my morale because I knew that I would recover the ground and go further.
Willpower, discipline and relearning good habits (or learning them for the first time, for some people) really are the boring secret. Most "diets" are harmful because a) they promise some kind of magical shortcut (which doesn't exist) and b) they are short-term, unsustainable regimes which don't teach you how to change for good. Even the diet plans which aren't harmful are mostly useful because of the structure they provide rather than any genuine logic or science behind them.
The paleo diet is a fad diet, really, but not a harmful one. If it gives you the confidence boost and structure you need, win.