On the bulletin board above my desk, I keep a handful of quotes that have taught me something, or that I hope to learn from.
There’s an awful temptation to just keep on researching. There comes a point where you just have to stop, and start writing.
I've never faced this problem from a nonfiction writer's point of view; I'm sure it's even more spot-on for them. The temptation to research, for me, is akin to a fear of starting. At some point, you really do have to start the work of writing.