A principle from G.K. Chesterton’s 1929 book The Thing: before removing something whose purpose you don’t understand, find out why it was put there.
The original passage:
In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, “I don’t see the use of this; let us clear it away.” To which the more intelligent type of reformer will do well to answer: “If you don’t see the use of it, I certainly won’t let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.”
The Argument
The fence didn’t grow on its own. Someone built it, which means someone had a reason. The reformer who sees no purpose is at minimum reporting their own ignorance — and possibly nothing more.
This isn’t conservatism. The principle doesn’t say don’t remove the fence. It says understand it first. Once you know the original purpose, you may find it no longer applies, or that the fence was a mistake from the start, or that it solves a real problem badly. Then you can remove it knowingly.
Application
Although stated in terms of social reform, the principle generalises. Don’t delete the weird-looking check, the legacy branch, or the abandoned-looking config flag without first finding out what it was guarding against. Procedures that look pointless often encode lessons from past failures the current generation hasn’t witnessed. The bizarre setting toggled on in production years ago probably fixed a real bug — one that will return the moment you turn it off.
The Generative Problem
The opposite error — building fences without recording why — creates the conditions Chesterton’s Fence is designed to address. Every undocumented decision becomes a future fence whose purpose is forgotten. Over time the codebase, the organisation, the institution accumulates fences no one understands and no one dares touch. Chesterton’s Fence is the rule for navigating that landscape. The discipline of recording rationale is what stops you from generating it.