A monad is like a tiger in a cage. You don't want it running around mauling all your code, so you transport it in cage. If someone needs your tiger for somethin

A monad is like a tiger in a cage. You don't want it running around mauling all your code, so you transport it in cage. If someone needs your tiger for something they need to have the key to his cage. Also it is polite to put the tiger back in the cage if anyone else needs him.