By default, our instinct is to conquer the fear, but our feelings are much, much, less within our control than the goals we set, and since it's the conflict BETWEEN the two forces blocking you, if you simply change your goal from "writing well" to "writing badly," you will be a veritable fucking fountain of material, because guess what, man, we don't like to admit it, because we're raised to think lack of confidence is synonymous with paralysis, but, let's just be honest with ourselves and each other: we can only hope to be good writers. We can only ever hope and wish that will ever happen, that's a bird in the bush. The one in the hand is: we suck.
We are terrified we suck, and that terror is oppressive and pervasive because we can VERY WELL see the possibility that we suck. We are well acquainted with it. We know how we suck like the backs of our shitty, untalented hands.
We could write a fucking book on how bad a book would be if we just wrote one instead of sitting at a desk scratching our dumb heads trying to figure out how, by some miracle, the next thing we type is going to be brilliant. It isn't going to be brilliant. You stink. Prove it. It will go faster.
And then, after you write something incredibly shitty in about six hours, it's no problem making it better in passes, because in addition to being absolutely untalented, you are also a mean, petty CRITIC.
You know how you suck and you know how everything sucks and when you see something that sucks, you know exactly how to fix it, because you're an asshole.
So that is my advice about getting unblocked. Switch from team "I will one day write something good" to team "I have no choice but to write a piece of shit" and then take off your "bad writer" hat and replace it with a "petty critic" hat and go to town on that poor hack's draft and that's your second draft.
— Dan Harmon