Are writers truly that humble or just ass-holes in disguise?

I often enjoy going to literary talks/readings where authors stand up and talk about their process and inspiration for writing. Being an individual who is hoping to some day become a writer, I always ask these successful authors the same question every time:
How did you know that you could write?
The question is often greeted with the humble chuckle and shaking of the head along with the statement that they "still don't know" or "doesn't actually think that they can write" and other sweet, humble little comments. Are they really that humble though?  A little bit of me almost doesn't believe that they are because there has to be some inclination, itch, voice-in-the-head, that whispers into a writer's ears "that is really good" and I don't care if that makes them sound like self-centered ass-holes, because it is at least honest. I want to know what that feeling is, what that voice sounds like, what the experience is when you write something that it at least halfway decent so I would at least be able to focus in on those feelings to give me some chance of actually improving my form. I know that practice and dedication are also part of it but there has to be something more than that.