I honestly don't know. I think, just my desire to write. But I write in irregular bursts (that reminds me, I need to start part 3 of Fitzjohn).

For example, with my Fitzjohn story (saga? tale? series? whatever), I wrote part 1, then almost immediately started on part 2. But it's been weeks, and I still haven't started part 3.

I like to read people's thoughts and ideas on the stories I write, and it's reassuring to hear they aren't utterly awful (so go comment on part 2 or I'll cry ).