What modern idiom describes Pandora’s box as a source of many unexpected troubles?

The modern idiom is “opening Pandora’s box,” meaning to start a process that causes many unexpected problems.

The expression comes from the myth in which Pandora opens a sealed container and releases forces associated with suffering into the human world. In modern English, the phrase is usually figurative rather than religious. It can describe an investigation, policy decision, technical change, or personal action whose consequences become difficult to control.

The idiom is often used with the verb “open,” as in “That decision opened Pandora’s box.” It does not normally mean that every consequence is evil or that the original action was intentionally harmful. Its central idea is that one seemingly limited action unleashes a much larger set of complications.

The wording also preserves the translation history of the myth. Hesiod’s vessel was a large jar, while later European usage popularized “box.” The idiom therefore combines an ancient narrative with a Renaissance-era translation choice.