Chesterton's Fence

> Chesterton went on to explain why this principle holds true, writing that fences don’t grow out of the ground, nor do people build them in their sleep or during a fit of madness.

Chesterton never had to maintain an old code base. People do "build fences" during a fit of madness, or maybe during a bout of incompetence. But even then his point is well taken, because it's hard to tell if a given fence was built by a madman or a drooling idiot.