I was listening to a podcast that had an interview with a food photographer. They asked the photographer why she takes pictures of food. The photographer answered "If I could answer that question fully I'd probably stop shooting what I'm taking pictures of".
I've long known that, for me, writing is therapy. I don't write what I know, I write what I'm discovering, what I'm learning. I write to work through my emotions, my stress, to help me comprehend what is going on and find organization to the chaos of life.
Maybe that's why certain pieces fall flat after awhile, there's no discovery there, nothing to learn, so the novel becomes stale and boring and is eventually left, figuratively dusty and alone, on the dropbox account.
What about you? Do you write what you know? Or what you want to know?