I used to do the same thing, beating myself up for slipping up and eating something I shouldn't. But now I've changed my whole way of thinking about diet and exercise. I'm choosing to eat right and exercise because it's the way I want to live, not because I want to get to some magical goal. If I were only doing this to get to a goal weight, I'd probably stop once I got there, and then go right back up. So now if I pig out or miss one day of exercise, it's no big deal, because I know that I'm doing this for the long haul. One day isn't going to make that much of a difference over the course of 50 (or more!) years.