"That's all the motorcycle is, a system of concepts worked out in steel. I've noticed that people who have never worked with steel have trouble seeing this...that the motorcycle is primarily a mental phenomenon. They associate metal with given shapes...pipes, rods, girders, tools, parts...all of them fixed and inviolable, and think of it as primarily physical. But a person who does machining or foundry work or forge work or welding sees "steel" as having no shape at all. Steel can be any shape you want if you are skilled enough, and any shape but the one you want if you are not. Shapes, like this tappet, are what you arrive at, what you give to the steel."