Raymond Chandler in a 1949 letter to Alex Barris on the discipline of writing:
What do I do with myself from day to day? I write when I can and I don’t write when I can’t; always in the morning or the early part of the day. You get very gaudy ideas at night but they don’t stand up. I found this out a long time ago….
I’m always seeing little piece by writers about how they don’t ever wait for inspiration; they just sit down at their little desks every morning at eight, rain or shine…. However blank their minds or dull their wits, no nonsense about inspiration from them. I offer them my admiration and take care to avoid their books. Me, I wait for inspiration, although I don’t necessarily call it by that name… The important thing is that there should be a space of time, say four hours a day at the least, when a professional writer doesn’t do anything but write. He doesn’t have to write, and if he doesn’t feel like it, he shouldn’t try. He can look out the window or stand on his head or writhe on the floor. But he is not to do any other positive thing, not read, write letters, glance at magazines, or write checks. Either write or nothing…. I find it works. Two very simple rules, a: you don’t have to write. b: you can’t do anything else. The rest comes of itself.