Chesterton’s Fence is the principle that reforms should not be made until the reasoning behind the current setup has been understood.
In G.K. Chesterton’s words:
There exists in … 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.
In simple terms, don’t ever take a fence down until you know the reason why it was put up!