Personally I don't find it difficult to stick to my diet even though it's very limited because the results of going off it are severe enough to provide strong motivation. Once I became used to it and learned how to cook things I can safely eat, it became a matter of simply defining myself as someone who doesn't eat certain foods no matter what. That's no different than knowing I'm the kind of person who would not steal someone's purse even when broke.
The most difficult part of the diet is the reactions of other people. When I visit homes or attend social functions someone usually tries to talk me into eating something and many act like it's a personal insult when I refuse. Many hostesses and some hosts seem to feel like failures if they can't provide something for every guest. I finally learned to request some ice water or hot water, whichever is most difficult for them to prepare. If they have to fuss just a little to fix me something that seems to satisfy most hospitable people so they'll let me eat the food I brought in peace.