How do you keep yourself in-check? This could mean your form on a given exercise, the quality of your meals, how much sleep you are getting, etc.
As an example I use, when I squat, I always record my working sets from the side on video. I do this to make sure I'm hitting the depth I need, plus to recognize if form is breaking down. If a weight feels good but I didn't 'own' it, I will either do it again or not go up.
Another example could be a food log or a daily journal. It's easy to check the box, but do you know you really did?