It's not necessarily a good thing, but it's the way things happen for me. A book springs into my head almost like the goddess rising fully formed from the sea. I know who the characters are, what's going to happen, and what mood I want to create.
Unfortunately, I have a zillion things to do besides write all that down, and I know from experience that it's an all-absorbing process that takes weeks, even months for just a first draft.
How do authors write while they're marketing the book(s) that came before? How do they find time to think, plot, create, and execute while making calls and writing letters, sending off press kits and ordering bookmarks? Oh, and there's that thing called Life that happens at the same time, so that feeding the cats and having actual conversations with friends is advisable, often necessary, for the sake of sanity.
It's yet another part of publishing that I'd heard discussed by fellow writers but never really grasped until now, when I'm in the midst of it. Understand, I'm not complaining. I wouldn't give it up, but I have a whole new respect for those writers who manage a book a year and still show up smiling for signings and readily respond to fans and followers. We're mostly solitary people, yet to be allowed to do what we love we must become public commodities. That book inside my head will have to wait, at least for today.