At the head of an incredible string of railroad cars—open-slatted cars for produce and closed refrigerator cars and flatbed cars for industrial steel and low-slung coal cars with hoppers underneath— there is an engine.
It may be we can fashion a metaphor from the hundred-or-more-boxcars-long freight train—a metaphor about progress. There are scores of diverse elements, but there is a driving force. Something is doing the pulling.
It doesn't happen by itself; there is an engine.
