Writer's block is a failure of authority
Norman Mailer says:
All writing is generated by a certain minimum of ego: you must assume a position of authority in saying that the way I’m writing it down is the only way it happened. Writer’s block, for example, is simply a failure of ego.
Alexander Chee says:
The writer stops writing when they believe the idea is fraudulent. When they believe the idea will trick them into making a mistake.
If you're experiencing writer's block, it's because you lack the confidence and self-possession to dictate the story as you see fit. The fact that you are writing it in the first place means you hold the authority: you are, quite literally, the author. Remember that ultimately this is your story1, your imagination doing the work, and readers will take your authority on face value.
Of course, the problem with it being your story is, as Dan Harmon points out, that you can see everything that’s wrong with it. But the only solution to that is to write more.↩