And here’s David McCullough:

There’s an awful temptation to just keep on researching. There comes a point where you just have to stop, and start writing. When I began, I thought that the way one should work was to do all the research and then write the book. In time I began to understand that it’s when you start writing that you really find out what you don’t know and need to know.

START BEFORE YOU THINK YOU’RE READY