Being an artist is more difficult than one would imagine. So much time, effort, and emotional and mental energy go into your chosen craft, and there is often infrequent external feedback or reward. Feedback does come, from time to time, but there can be a lot of long spaces in between.
So, all the more reason that large quantities of internal motivation are needed. It's funny to me when I meet the rare artist who isn't very internally driven. I've met only a few, and they appear to have let almost all of their creative processes be dictated by externals. But what's difficult is when the externals they were counting on dry up, they seem lost and not sure how to move forward.
Although it can ebb and flow, I seem to have large quantities of internal drive. And, I guess that's a good thing, because if nothing else it helps to sustain creative thought and process over the long haul. Even in the dry periods, internal motivation is like a pilot light burning in the darkness, waiting to be put into operation.