According to Greek legend, the first woman, Pandora, was actually sent as a curse to Zues' men (See, you knew it was true, guys) and was given
a present upon her marriage. The present was a box that
she was told never to open. Needless to say her curiosity got the better
of her (like eating forbidden fruit) and she unleashed eight demons unto the world. The first seven
being the seven
deadly sins, and the last, which she managed
to capture, was hope.
Today, much like christianity's idea of biting forbidden fruit, opening pandora's box refers to getting
into a situation
over which one has very little control over.