“When you make the two one, and when you make the inside like the outside and the outside like the inside, and the above like the below, and when you make the male and the female one and the same, so that the male not be male nor the female; and when you fashion eyes in the place of an eye, and a hand in place of a hand, and a foot in place of a foot, and a likeness in place of a likeness; then will you enter the Kingdom” (Jesus Christ, Gospel of Thomas).
In many folklore traditions, mythologies and fairy-tales around the world, characters have to overcome or endure certain trials as a penance, to prove their worth (to marry a princess, for example), break a curse or claim their ultimate prize. These trials may be extremely hard (The Labours of Hercules) or even impossible to overcome or solve. At one end, there are riddles to be guessed, such as the famous riddle of the Sphinx from the Greek mythology (“What walks on four legs in the morning, two legs in the afternoon, three legs in the evening, and no legs at night?”) or the puzzles in the stories of Persian poet Nizami, which also found their way to Puccini’s opera Turandot, but another extreme is a truly impossible task set to frighten and confuse characters or heroes. These paradoxical, “undoable” commands often have a wondrous effect.
I. The Innocent Anthropologist: Notes from a Mud Hut [1983] by 
Thoughts on Papyrus 