Imagine a giant factory, with big machines pouring hot metal and pounding it into shapes and then feeding things from one machine into another, connected by conveyor belts (at various speeds) and pipes (with various valves.)

One day, after the whole place was shut down for renovation, the manager comes in and gasps in shock: The Master Manual is gone, which means nobody knows what machines to warm up first, what valves to open or close, and whether Smasher 27-B needs to be showing the blue light or the red light when Puller 8C moves the whimble arm.

Now imagine that somebody lost or destroyed all the manual which tells which machines and conveyor-belts and pipes have to be started and in what order to do it safely.