Writing motivation

In the past two days I've had three different people ask me how I motivate myself to write when I have so many other things to do with my life. Including my mother. What is it that compels me to write in every free moment I can find between a fairly demanding job, kids and trying to maintain a home?

So I've been thinking about it, and you know what? It's not all that easy to answer. It's not like I have a deadline to meet, or any reader expectations yet. The acceptances are nice, but they're few and far between. Especially lately, since I've been so focused on novel writing, I haven't even submitted any short stories to publications.

I guess the honest answer is, I can't stop. Writing is like breathing. I'd feel funny if I didn't do it every day. I keep telling myself one day I will be able to go to my local library, look under 'L' and find my book sitting there, along with all those other great 'L' authors. That dream is enough to motivate me to sit down in front of my computer again, open up the document I've trawled through hundreds of times already, and try to cast an objective eye across it one more time.

I have to admit though, with winter approaching and the days getting shorter, that hour in the mornings before the kids get up is getting harder. I'm not sure how I'll handle it once the temperature drops too, and I'm forced to sit, shivering over the keyboard in three layers of sweaters and gloves. But I'll keep that vision of my book cover in mind, and I'll shiver my way through winter. Hopefully by then, the builder will have replaced the missing walls....

How do you motivate yourself to write? And do you ever find your drive to create flagging?