I am self doubting hard and it is making me unable to write, thinking I'll ruin what I've written so far!!
I have, somewhat, conquered said self doubt in my self by doing two things. Although they might not work if writing is your job.
1st I don’t bother writing if I don’t feel inspired to. If not I will focus on a small mistake and try to rewrite everything up to that point. So, now, instead of uselessly picking apart my old work, I now have a bad habit of thinking too much about what could happen next in the story and why. Eventually, after a couple days/weeks, I feel it and write a scene before it slips from my grasp, other times I can write a 10 thousand words with no sign of stopping. After that I outline what should happen in the next couple of scenes/chapters.
2nd I have a standard of quality I wish to achieve before I publish. If I do my best then there will be little for myself to fret about. Although that means it might further delay my releases. Every month or so I begin writing and/or coming up with something new, but that never is seen here because I want more words, better scenes and dialogue, little or no spelling mistakes, good and consistent characters, etc. When I break said standard I feel awful. Two months ago I thought doing this was counterproductive since I couldn’t improve without outside opinion, so I wrote like 5,000+ words using a story idea I had before doing a very light edit and publishing it, and not looking back. Quite frankly it wasn’t up to my standard and had a bunch of easy mistakes. Hell, I even misspelled a character’s name in the title and didn’t realize it for 2 weeks. So I keep my stories private until I feel they are ready to share.