What modern expression means an action that releases many unexpected problems, like Pandora’s container?

The modern expression “opening Pandora’s box” means taking an action that releases many unexpected problems.

The idiom comes from the popular form of the Greek myth in which Pandora opens a sealed container and allows the world’s troubles to escape. In everyday English, it is used figuratively for an apparently simple decision that produces complicated, harmful, or uncontrollable consequences.

The expression is not limited to mythology or literature. Journalists, historians, scientists, and policymakers use it when discussing a risky discovery, controversial decision, or new technology whose effects may be difficult to reverse. Its meaning is usually cautionary rather than literal.

A common historical correction is that Hesiod’s original vessel was a pithos, or large jar, not a box. The idiom nevertheless uses the later box tradition because that version became dominant in European languages. “Opening Pandora’s box” should also not be confused with “hope remains,” a separate interpretive issue concerning whether hope was inside the vessel or stayed outside after the other troubles escaped.