Perfectionists have a hard time starting things and an even harder time finishing them. At the beginning, it's they who aren't ready. At the end, it's their product that's not. So either they don't start the screenplay or it sits in their drawer for ten years because they don't want to show it to anyone.
But the world doesn't reward perfection. It rewards productivity. And productivity can only be achieved through imperfection. Make a decision. Follow through. Learn from the outcome. Repeat over and over and over again. It's the scientific method of trial and error. Only by wading through the imperfect can we begin to achieve glimpses of the perfect.