That's what I'm fighting now. When I look at a keyboard, or a pen, or blank sheet of paper the least helpful part of my brain starts talking. Nothing I have to say is important. Nothing I want to write is worthwhile.
Fighting that voice gets much harder when I do the silly thing and compare myself, often to other writers I know or admire. So now I have to scrap that voice forever and start fresh.
What I have to say is worthwhile.