Quentin Tarantino said that "directors never finish their films, they abandon them."
One of the biggest challenges to achieving excellence is the little voice inside your head that warns you that your efforts aren't good enough. Self-awareness and introspection are crucial to growth, but it's easy to fall into the trap of being your own worst critic.
"Paralysis by analysis" can tie you up in knots, and interfere with your ability to be productive.
Even today, when working on projects, prior to submitting them to my clients, a little voice inside sometimes thinks "Oh god, this is shit. I can't hand this in!"
Fortunately I've learned to give that little voice no power. I know that my work is appreciated, so listening to irrational fear instead of the positive feedback of others makes no sense.
If you hold off on getting something completed until it's "perfect" then you risk never accomplishing anything. At the very worst, you're better off doing something, anything, than doing nothing.
By all means, look for opportunities to improve and accept constructive criticism, but it's just as important to believe in yourself, believe in the value of what you can do, and go do it!