One of the most important things we need to remember is to to forgive. Ourselves, each other.
We need to forgive ourselves when we do something we promised ourselves we wouldn't. Whether it's not following a nutrition plan, missing workouts or staying in a relationship that's toxic. We need to accept the fact that we're not perfect and that we'll do things from time to time that we didn't want or mean to do. So forgive yourself, move on and do your best going forward.
I'm not sure if it's harder to forgive ourselves or others. But people are human. We all make mistakes. Some worse than others. And yes, there are things that are basically unforgiveable. And everyone's definition is something different. But try to forgive others because one day, we're going to need someone's forgiveness for something that we did ... intentional or not.
All we can do is try to be the best person that we can possibly be. Warts and all :)