Chesterton’s fence
Etymology
From a 1929 passage by G.K. Chesterton: a reformer who wants to clear a fence across a road should first find out why someone built it. His name became attached to the rule — an eponym, not an ancient root.
noun · /CHES-ter-tunz fens/
The principle that you shouldn’t remove a rule or structure until you understand why it was put there.
What it names
A guard against confident reformers — the reason a thing exists may not be obvious, and tearing it out can carry hidden costs.
Example
Before deleting the "pointless" approval step, remember Chesterton’s fence — someone may have added it after a costly mistake.
Related idea
Second-order effects are exactly what Chesterton’s fence warns you to check before acting.