Starting a story with ‘Once upon a time’ does not guarantee a happy ending. In their classic collection of folk tales, the rather aptly named Brothers Grimm made sure there was a moral to every story: goodness is rewarded, evil is punished, sometimes quite brutally. Even Hans Christian Andersen’s stories do not all end happily ever after: the prince who disguised himself as a swineherd to test the princess’s devotion came to despise her and returned alone to his own little kingdom.