The principle in public policy that reforms should not be made until the reasoning behind the existing state of affairs is understood.
Chesterton’s Fence is a heuristic inspired by a quote from the writer and polymath G. K. Chesterton’s 1929 book, The Thing.
I’ve written about how this applies to writing technical documentation for software projects at Chesterton’s Fence and tech documentation : Juha-Matti Santala