a bad habit of crying for the moon

Well, as you may suppose, the war was over before it was begun, the Old Wise Person being found. When it was discovered that she had taken Knuta away to cure him of a bad habit of crying for the moon, and had merely forgotten to return him before, she was forgiven; and the Next Door King and Erranta’s father became close friends, as well they might when the son of the one married the daughter of the other.

From “The Wandering Princess” in The Magic Book of Fairy Tales published by Bracken Books in London (1986) as a reprint of More New Fairy Tales by Blackie and Son, London.