I used to preach that a writer must be disciplined. Seat of the pants to seat of the chair. Write every day. Blah, blah, blah. I no longer believe that.
Writing is a matter of desire, not discipline. If you want to write, that's what you'll do. If you want to write you'll rearrange the circumstances of your life to make it possible.
If you want to write, you can't not write.