Writing a novel is like making a movie: All sorts of accidental things will happen after you’ve set up the cameras. So you get lucky. Something will happen at the edge of the set and perhaps you go with that. You come into it accidentally. You set the story in motion, and as you're watching this thing begin, all these opportunities will show up. So in order to exploit one thing or another, you may have to do research. You may have to find out more about Chinese immigrants, or you may have to find out about Halley’s Comet, or whatever, where you didn't realize that you were going to have Chinese or Halley’s Comet in the story. So you do research on that, and it implies more, and the deeper you get into the story, the more it implies, the more suggestions it make on the plot. Toward the end, the ending becomes inevitable.