I've never fallen off the wagon, although I had some spectacular cheat days when I first started (about once every week or two). Then I went through a couple of months where I had desserts 3-4x per week.
Now, about 1.5 years into Paleo, it's easy for me not to cheat, because I really don't like how I feel when I have gluten or vegetable oils.
Paleo has never been something that I've TRIED to do or that I forced myself to do. It's never been a sacrifice or a chore or a diet.
For me, life on Paleo is like getting to drive a well-tuned Ferrari or a Bugatti every day. I could take the broken-down Yugo out for a spin once in a while if I like, but it's really not that enticing.
I consider myself one of the lucky ones. Whenever I've tried lifestyle modifications in the past, they were very difficult for me to stick to, so I sympathize with everyone who has a hard time sticking to Paleo.
I think the trick is that I want the benefits so badly that I'm willing to do most anything to get there. I really want that 400-500lb. deadlift. I really want to feel great every day and not have gas and diarrhea. Luckily, I found something that
- makes a lot of sense (think about health/nutrition through the lens of evolution)
- works really well
- is relatively easy to follow (eat this, don't eat that, eat when hungry)
- has awesome implications for long-term health (diabetes, cancer, stroke, Alzheimer's are not fun ways to go).
So really, it's a no-brainer. It's not hard for me. I wish I could find ways to make it easier for other people who struggle with this.