What modern idiom describes an action that unleashes many unexpected problems, like Pandora’s container?

“Opening Pandora’s box” describes an action that unleashes many unexpected problems.

The idiom comes from the myth in which Pandora opens a container and troubles spread into the human world. In modern English, the phrase is usually applied to a decision, investigation, policy, or invention whose consequences become difficult to control.

The expression is metaphorical rather than a literal claim about mythology. Someone may say that a new legal case, technology, or political dispute “opens Pandora’s box” when it creates additional complications beyond the original issue. The phrase normally suggests that the consequences are numerous and hard to reverse.

A common mix-up is treating the idiom as evidence that Hesiod described a hinged box. The English expression became established through later translation and reception, while the original Greek account used pithos, a large jar. Both the myth and the idiom remain widely recognizable, but they belong to different stages of the story’s history.