You already know, and have stated it here, but I want to double up on it. Drinking, diet, wanking, smoking, ... If you fuck up for a day, tell yourself "Man, that was a stupid choice. I'll feel less shitty tomorrow, when I get back on the path." Then, get back on the path, forgive yourself for yesterday, and let it go. (Of course, if your choice has led to hospitalization or incarceration, you might want to put a reminder on a post-it somewhere visible.)