Every action you make should be treated as its own, separate from all other actions/decisions that you’ve made leading up to it. Think of there being a reset button for every action that you take. This will help give you a clearer vision of what step you need to take next.
Before acting, you need to think of the consequences of your actions. Will you be happy with those direct/indirect consequences?
For example, if you’ve made a series of bad decisions on your diet one day, you can think one of two ways. You can either say, “Screw it. I’ve already eaten poorly today, I’m just going to continue to eat poorly and then I’ll start over tomorrow.” OR you can hit that reset button right now and say, “Wow. I really haven’t eaten well today. I need to refocus on what the end goal is (better health, better body, clearer thinking, etc) and then eat accordingly.”
The above example is meant to illustrate that you can turn any choice around and you get to decide how you’re going to change your life. That’s not to say that you can’t/shouldn’t treat yourself from time to time, but you need to be cognizant of the trade offs when doing so.