What modern expression means an action that releases many unforeseen problems, echoing Pandora’s myth?

“Opening Pandora’s box” means taking an action that releases many unforeseen problems. The expression comes from the myth in which Pandora opens a vessel and allows evils to escape into the human world.

In modern English, the phrase can describe a political decision, a scientific discovery, a legal dispute, or any other step whose consequences become difficult to control. It usually warns that investigating or changing one thing may unleash a much larger set of complications.

The expression is related to, but not identical with, “opening a can of worms.” Both suggest creating trouble, but “opening Pandora’s box” specifically invokes the Greek myth and often emphasizes consequences that were previously hidden. “Crossing the Rubicon” instead refers to an irreversible decision, while “meeting one’s Waterloo” means suffering a decisive defeat. These neighboring idioms should not be treated as synonyms in every context.