Maybe, self-doubt is an indicator of aspiration?
You might sit drown and write every day, for example.
In this action, you are doubtful of your ability, you are doubtful of both the quantity and quality of your work, and you might even be paralyzed with the idea of sharing your work.
It is because writing is your passion.
You don’t sit and worry about your abilities as an astronaut, or plumber, or computer programmer, do you?
“Self-doubt can be an ally. This is because it serves as an indicator of aspiration. It reflects love, love of something we dream of doing, and desire, desire to do it. If you find yourself asking yourself (and your friends), “Am I really a writer? Am I really an artist?” chances are you are.”