(noun) A principle that states one should not remove or change something (like a fence, rule, or tradition) until they understand why it was put there in the first place.

Before the team decided to remove the legacy authentication system, they invoked Chesterton’s fence and spent time understanding why it was originally implemented that way.

The concept gained widespread recognition through Shane Parrish’s influential article “Chesterton’s Fence: A Lesson in Second Order Thinking” on Farnam Street.

The principle is named after G.K. Chesterton, who wrote in 1929: “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.’”

Examples:

• Questioning why a seemingly redundant code review process exists before removing it
• Understanding the historical context of a business rule before changing it
• Researching why a particular architectural decision was made before refactoring it
• Investigating the purpose of an old database constraint before dropping it