David Lynch commenting on how his ideas come together. I have experienced the same process with a central idea serving as a magnet for all the other ideas:
Sometimes if I listen to music, the ideas really flow. It’s like the music changes into something else, and I see the scenes unfolding. Or I might just be sitting quietly in a chair and bing! – an idea will hit me. At other times, I might be walking down the street when I see something that’s meaningful and inspires another scene. On anything that you start, fragments of ideas run together and hook themselves up like a train. Those first fragments become a magnet for everything else you need. You may remember something from the past that’s perfect, or you may discover a brand new thing. Eventually, you get little sequences going. Before you think of anything, the whole landscape is open. But once you start falling in love with certain ideas, the road you’re on becomes very narrow. If you concentrate, ideas will come to that narrow road and finish it.