I agree so much with this. You need "cold eyes". One important function of copy editing is to check your assumptions, and make sure everything is explained that needs explaining. That's almost impossible to perform on one's own writing and thought, because everything you know seems obvious, and everything you assume has become the natural and invisible given. Note how many people Paul Graham cites as reading his essays. Lots. Smart people. That's one reason why the essays are so good. It takes a village, or at least a smart friend, to write something good. It doesn't float out of your brain as a perfect work of art.