People who attempt to write a book (or a short story, magazine article, movie, poem, or song) harbor the belief that they can pull it off. They’ve convinced themselves they can spend the requisite time in a chair, are confident they can string together the necessary number of words, and trust they can slog through the revisions and rewrites required.
Believing in yourself is a good thing. An essential thing. Without that belief, no word would ever get written.
But believing in yourself is only half the story.
It is equally important, perhaps more important, that you doubt yourself.
I think that bears repeating: If you want to be a writer, you must doubt yourself.
You must question every word. Is it the best word? Would another word say it better?
Would a metaphor, a simile, an allusion, or other indirect way of telling something work better than saying it straight out?
Is that the way this character would say that? Do you really think that character would do this?
And so on.
Writing—at least writing well—is a continuous process of self-doubt. And that’s just as important—if not more so—than believing in yourself.