In the idiom “open Pandora’s box,” what does the box metaphorically release?

In the idiom “open Pandora’s box,” the box metaphorically releases unforeseen troubles.

The expression comes from the Greek myth in which Pandora opens a sealed storage jar and destructive forces escape into the human world. In modern English, saying that someone has “opened Pandora’s box” means that an action has created many unexpected problems or consequences that are difficult to control.

The idiom is commonly used for discoveries, decisions, investigations, or technologies that produce complications beyond their original purpose. It does not usually refer to one isolated problem. The emphasis is on a chain of troubles emerging from a single act.

The expression also preserves a historical mistake. Hesiod’s original container was a pithos, or large jar, but the familiar word “box” became established through later Latin and European retellings. The modern idiom therefore combines an ancient story with a later translation tradition.