Agent Maria Carvainis told me many years ago that authors are the most egotistical people she knows -- the most insecure.
And for most of us, she's right on target. Think about it: it takes a whole lot of confidence for someone who's never written a book to decide that a) they can do it, b) someone will want to read it, and c) they can make money with it. If writing wasn't a passion, if they didn't believe in their stories and themselves, they would never start.
So they pen the next great American novel, and sooner or later they let someone read it: a relative, a friend, a critique partner, an agent or an editor. Generally, then comes the rude awakening. That great novel turns out to be nothing but a semi-coherent mishmash of stuff that no one who doesn't love her dearly wants to read.
It can be devastating. I cried for two days when I got my first rejection. I swore I would never write again. I thought I had talent, and the editor ended her less-than-glowing letter with "don't bother me again."
That's where the wannabes get separated from the real writers. Real writers don't give up. Real writers learn what they can from the rejection (I learned not to submit to that particular editor ever again), and then they go right back to writing. For me, it was the day I discovered I couldn't resist the challenge. I was going to show her that I did, too, have what it took to be a writer. (Keep in mind, I'd been successfully resisting other challenges, like exercise and diet, for many years, so this was a real eye-opener.)
You have to have that ego, to think that anyone out there could possibly be interested in what comes out of your head, and you have to have that insecurity so you never grow complacent. You never get comfortable. You keep learning and striving and challenging yourself. You want every book you write to be better than the one before. (If you're reading this while in the middle of complete revisions, trust me, you do want it to be better, even though right now you just want all the characters to die and give you peace.)
It's a balancing act -- that ego sweetly whispering in your ear, "You're the best ever," and that insecurity curled in a ball in the corner of your brain shrieking, "You can't do this! It was a fluke! They'll find out you're a fraud!"
But, in my never-humble opinion, it's the best gig out there.