Chesterton's Fence is an argument put by author and political thinker G. K. Chesterton about considering the usefulness of traditions.
It can be simplified as:
A reformer approaches a fence across a road and says "I do not see the use of this fence, let's tear it down," to which a more intelligent reformer says, "let us first assess the purpose of this fence, and then once we understand its purpose, we can decide again whether to tear it down."
Chesterton's Fence is an illustration of the Einstellung Effect. The man wanting to tear down the fence might consider himself an intellectual for thinking analytically about the pros and cons of the fence, however, it never occurred to him to think about the most important question of why the fence was set up in the first place.