Because writing, unlike a lot of other work, can eat your life. You can spend all your waking hours doing it. Especially if you love it and you don't have another reason to go out. Like a job, where you work for someone else.
Writing is hard work. It's harder work than I ever thought it was when I was lusting after a career as a writer. I remember telling Warren Ellis once that a novel was a demanding mistress. I have learned that lesson very well for myself now. It makes me understand why Ursula Le Guin is annoyed with the Google book project. It's the amount of work and expertise that goes into writing something truly valuable. It would be hard to see that work out there for everyone to access freely, especially if you were of a generation which grew up well before the advent of the Internet Age.
It's not just a talent. It's an artistic problem. It requires an individual sort of genius. It's complex, composed of layers of words, rhythm, meaning, plot, character, theme, tension, and intrigue. If you were to ask me when I write, my answer might be that I write from 10 in the morning until 2 a.m. That is, all my waking hours. But a more accurate answer is that I write in my sleep -- wake up in the middle of the night with an idea for how to solve a problem in my novel and jump up to write it down before I forget it. I write when standing in line at the corner shop. I write as I walk down the street, putting images into words in my head:a woman balancing, straight-backed as she rides a bicycle, the mottled color and pebbly texture of a brick wall, the color of the sky before a thunderstorm. I can't guarantee that there's any time when part of my brain isn't working on the problem of writing.
I suppose I write this post to caution young writers who would let writing devour their lives before they have anything to write about. I'm going to try again to take a day off per week. Because woman cannot live by writing alone. But if I fail at this, I'll definitely take a break after I finish this novel. Which should be any day now.
Famous last words.