The alternative is nothing

Here is Raymond Chandler‘s take on Getting Things Done, as found in Willpower: Rediscovering the Greatest Human Strength, by Roy Baumeister and John Tierney:

“Me, I wait for inspiration,” he said, but he did it methodically every morning. He believed that a professional writer needed to set aside at least four hours a day for his job: “He doesn’t have to write, and if he doesn’t feel like it, he shouldn’t try. He can look out of 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.”
[...]
“Write or nothing. It’s the same principle as keeping order in a school. If you make the pupils behave, they will learn something just to keep from being bored. 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.”

This is an interesting approach and it apparently worked for him to some extent, given his productivity as an author. The aforementioned book also explains why this would have worked:

The Nothing Alternative is a bright-line rule: a clear, unmistakable boundary [...]. Chandler’s particular rule – If I can’t write, I will do nothing – is also an example of an implementation plan, that specific if-x-then-y strategy that has been shown to reduce the demands on willpower.

He made it a personal policy, essentially resolving to not allow himself any other real options, during the time that he dedicated to writing.