You have to let go of the idea that your health is made or broken by a single day, and that each time you go off your diet you have to start all over again. Thinking this way severely discredits your past self. Think of all the work and living that past-you did to bring you to the point that you are at now. Your health, your whole being is a collection of choices made over weeks, months, and years. You don't get to start over. You just get to keep going. So if you fail, you only fail for a day, not for all time. It's a long road, but that's the fun part. :)