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.”

Chesterton’s Fence is a heuristic inspired by a quote from the writer and polymath G. K. Chesterton’s 1929 book, The Thing. It’s best known as being one of John F. Kennedy’s favored sayings, as well as a principle Wikipedia encourages its editors to follow. In the book, Chesterton describes the classic case of the reformer who notices something, such as a fence, and fails to see the reason for its existence. However, before they decide to remove it, they must figure out why it exists in the first place. If they do not do this, they are likely to do more harm than good with its removal. In its most concise version, Chesterton’s Fence states the following:

Do not remove a fence until you know why it was put up in the first place.