When we traverse the city, and imagine something like the subway, urging through the earth at high speed, we realize that a lot of our contrivances are merely some caveman's dream worked out over millenia. But noone ever dreamed diamond plate, and if they did, it was after the fact. Its presence--announced by the soft clatter of steel under our feet--attests to a hole in our dreams, our inability to think up every detail beforehand when planning out the adventure of our desire.