Chesterton's Fence
Chesterton's Fence is a principle of reform and change management articulated by G.K. Chesterton in 1929: before removing or changing any element of a system, you must first understand why it was put there. If you cannot state a reason for its existence that makes sense, you are not qualified to remove it — because the original reason may be invisible but important. The principle guards against the confident destruction of mechanisms whose purpose has been forgotten.