I've been a professional writer for much of my life, in the sense that for periods of time I've actually been able to eat and pay NYC rent by virtue of people paying me to write things.
But I don't know if I have a book in me. Because every time I try to write things that could possibly turn into a book I read them and they don't sound very good. I know what I'd have to do to change that, namely write a lot every day for a few years until it clicked. But I don't.
But so far I haven't made that a priority, so whatever book might be in me is still there. I think there's a lot of people like that. Many people just can't write and tell stories at all, of course. But many many people can, and would in fact be able to do so compellingly, but they haven't and won't put in the work.