I get really agitated with myself when I "blow it." I am on the verge of that today...cold, work stressed, scale not friendly over the past weeks even though I've been good...it's easy to just say, forget it, today's a wash. In the past if I messed up during the day, I would give myself free reign to go hog wild, figuring it was down the tubes anyway! Some people are chain smokers; I became a chain snacker once I crossed the line!
Getting past that is hard. Usually I try to take an accurate look at how big the mess up was. If I went over my calorie allotment, for example, I would feel like I failed, but sometimes it was only by, like, 150 calories (yeah, sometimes more). But I started to remind myself that I have a choice at this time, just like mambogirl said before me. You can acknowledge that it wasn't the way you wanted, but you didn't die and the world didn't end. It also helps me to think of ways I can "make up" what slipped...sometimes the next day, sometimes over the course of a few days or a week, with upping the exercise and being extra careful about food on other days. That makes me feel more in control.
I think that the quote I have in my signature is the most helpful thing that helps me get past those times. It just hits the way my mind works so exactly that I can't argue with the logic.
Take it easy on yourself, move forward, small steps. As long as you stopped making bad choices, you're further along now than you were when you were slipping off the wagon
. If you are so strict that you don't give yourself permission to goof a little, that's not a lifestyle you can live with!