Chesterton's Fence

Reforms should not be made until the reasoning behind the existing state of affairs is understood.

This principle is relevant in software engineering when removing technical debt. Each line of a program was originally written by someone for some reason. Chesterton's Fence suggests that one should try to understand the context and meaning of the code fully, before changing or removing it, even if at first glance it seems redundant or incorrect.

The name of this principle comes from a story by G.K. Chesterton. A man comes across a fence crossing the middle of the road. He complains to the mayor that this useless fence is getting in the way, and asks to remove it. The mayor asks why the fence is there in the first place. When the man says he doesn't know, the mayor says, "If you don't know its purpose, I certainly won't let you remove it. Go and find out the use of it, and then I may let you destroy it."