The principle that reforms should not be made until the rationale (if any) behind the current state of affairs is understood. (From G.K. Chesterton.)

“[...] a fence or gate [is] 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.”