Pandora's box is a story in Greek civilization. It happened after the kind Titan, Prometheus, stole fire for mankind, and was bound to a cliff where an eagle pecked out his liver each day as a punishment.
But Zeus, being Zeus, is not satisfied by the harsh punishment. Now that men have fire, he must punish them also for using this sacred object from Mount Olympus.
Before, there were no evil among men. They did not age, or die, or fight among themselves. But now Zeus decided that he will release all of these things into the mortal world.
Prometheus, being wise, knew that Zeus was planning this, so he warned his brother, Epimetheus, not to receive any gifts from Zeus. But sadly, Epimetheus had forgotten all about it when Zeus did give him a gift.
It was the first woman. She was carved by Hephaestus from a block of white marble, her lips from rubies, and her eyes from sparkling sapphires. Athena breathed life into her and dressed her in elegant garments. Aphrodite decked her with jewels and fixed a smile on her scarlet lips. Last but not least, Zeus named her Pandora, granted her curiosity, and a sealed pithos, or jar (not box!and warned her to never open it.
Hermes brought her to Epimetheus as a gift from Zeus, which he accepted despite his brother's warning. They married and lived together.
Though Pandora still couldn't be satisfied, since she had no idea of what was inside the jar Zeus gave her. The question drove her mad with curiosity, and finally, when Epimetheus was out, she decided to open it.
As soon as she lifted the lid, swarms of miseries came out: Greed, Death, Old Age, Envy, Disease, Lies, all roamed free on earth and possessed men. They became evil. They lied and stole and killed each other.
Pandora, now horrified by what she had done, closed the lid of the jar, just in time to trap Hope inside. Zeus sent a great flood to wash away all the evil men, leaving just two mortals who were still kind. But the horrors Pandora released still plague mankind to this day.
Moral? Well, if Zeus was kind enough to tell you not to open the jar, why don't you just leave it at that?