There's No Train Without the Tracks.

"Gandy dancer" is a slang term used for early railroad workers who laid and maintained railroad tracks in the years before the work was done by machines. Though rail tracks were held in place by wooden ties and the mass of the crushed rock (ballast) beneath them, each pass of a train around a curve would, through centripetal force and vibration, produce a tiny shift in the tracks. If allowed to accumulate, such shifts could eventually cause a derailment; work crews had to pry them back into place routinely.