I might spend 100 pages trying to get to know the world I'm...

I might spend 100 pages trying to get to know the world I'm writing about: its contours, who are my main characters, what are their relationships to each other, and just trying to get a sense of what and who this book is about. Usually around that point of 100 pages, I start to feel like I'm lost, I have too much material, it's time to start making some choices. It's typically at that point that I sit down and try to make a formal outline and winnow out what's not working and what I'm most interested in, where the story seems to be going.