The concept of progress not perfection is the idea that consistent progress towards your goal is better and far more productive than trying to pursue your goal to perfection.
The premis behind the concept is the fact that perfection is impossible for you to achieve and by pursuing perfection you are in fact pursuing the impossible. Dooming your efforts to failure from the start. (You can see where this can leads you down a path of fear, doubt, procrastination, and other limitations).
However, by pursuing consistent progress you are freeing yourself from the need to do something perfectly. You are allowing yourself the gift of making mistakes and using them as learning opportunities. This helps you to get started and gain momentum while making some kind of progress towards your goal.