A casual statement by my friend Steven Savage stuck in my mind: "There's something to how writers are more than writers, and fail themselves by only being writers."
A little background is in order. The two of us had been talking about something I bring up a lot — how any artist needs to get outside the bubble of her own particular discipline and learn how things work elsewhere. I learned far more than I ever expected to about my own creative discipline by reading about how music producers did their jobs, or how Tadashi Suzuki and Ze-ami worked with actors. The point is to get away from all of your suppositions about how things need to be and why, and see how that shakes you up.
When Steven said that writers fail themselves by only being writers, I took that to mean that they were short-changing themselves of all the other things that go with being creative: marketing yourself; coming to a better understanding of the worldview that informed one's own work (essentially, becoming a thinker and not just a creator); and drawing on other creative disciplines. Nobody ever just writes, and the more conscious you are of it, the better you'll be at it.
I also see this process as a way to avoid the so-called "expert beginner" problem, where someone plateaus at a certain level of their creative development. They don't know how to push themselves further, or they don't have anyone challenging them to up their game, and so they don't bother. As the author of the piece that originally made me aware of this issue wrote, they don't have ten years of experience, but the same year of experience repeated ten times.
Various theories come to mind about how this happens. First is sheer ignorance: people don't know how to push themselves, or even why. Second is arrogance: they already see themselves as having "arrived", so they don't need to do any more painful growing. A third one, which is akin to the second, is that people who have an unchallenged self-image of themselves as artists will do as little as possible to challenge that self-image — they like to think of themselves as being creative, without really embracing creativity as an iterative process of self-improvement as well as a process of creating external artifacts. I couldn't have written the books I have now ten years ago, because I wasn't the person I was ten years ago. Writing the books I wrote ten years ago helped me become the person I am now, to write the books I can today.
So maybe that's what it's all about. Just being a writer, in Steven's words, means missing out on being a full-blown creator.