Some, including famous authors, say they don't. Real writers just know, they keep going. They never question WHAT THE HECK they're trying to accomplish or who they're kidding. I want to believe this at times, but I'm still stuck in reality.
Everyone has doubts. Our mailman wonders if he should retire or work a few more years. Your waitress worries about being a good mother while attempting night school. Many thoughts for people are specifically dealing with jobs; we're occupied by our occupations.
The majority of writers don't get paid, must juggle another job, have people in their lives thinking they're crazy, and may never feel validated in a meaningful way in an area they want very much to succeed in. I am worried about the writers who are so assured they ALWAYS sleep easy. Nothing important should be so light upon the mind.
I doubt, worry, question, fidget, examine. Does it make me a lesser writer? Only if it stops me for good. Only should it censor my content.
What is your current "doubt level"? What occurrences make it worse?