For the pleasure of pedantry I will call it the Doctrine of Conditional Joy. Touchstone talked of much virtue in an “if”; according to elfin ethics all virtue is in an “if.” The note of the fairy utterance always is, “You may live in a palace of gold and sapphire, if you do not say the word ‘cow'”; or “You may live happily with the King’s daughter, if you do not show her an onion.” The vision always hangs upon a veto. All the dizzy and colossal things conceded depend upon one small thing withheld. All the wild and whirling things that are let loose depend upon one thing that is forbidden.
From “The Ethics of Elfland,” chapter III in Orthodoxy by G.K. Chesterton [Note to self: Touchstone is the court fool in Shakespeare’s play As You Like It.]