What phrase describes a seemingly small action that causes widespread trouble, like opening Pandora’s box?

The phrase “opening a Pandora’s box” describes starting a process that releases many unexpected problems. It comes directly from the myth in which Pandora opens a container and troubles spread into the human world.

In modern English, the expression usually describes an action whose consequences are difficult to control or reverse. It can apply to politics, technology, legal disputes, scientific discoveries, or personal decisions. The phrase is figurative rather than a claim that a literal magical box exists.

The wording reflects a long translation history. Hesiod’s original Greek account refers to a pithos, a large jar, while the “box” formulation became established in later European retellings. The idiom therefore preserves the familiar modern image even though it does not reproduce the vessel named in the earliest source.