What modern expression means opening a situation that releases many unexpected problems?

“Opening Pandora’s box” means starting a situation that releases many unexpected problems.

The expression comes from the Greek myth in which Pandora opens a container holding evils or troubles. Once released, these afflictions spread through the world. In modern English, the phrase is usually figurative rather than literal: an action may expose complications that were previously hidden or difficult to control.

The wording became especially influential through later translations and retellings that changed Hesiod’s pithos, or large storage jar, into a box. The phrase now appears in journalism, politics, law, business, and everyday conversation. It often warns that investigating or changing one issue may create several additional consequences.

“Achilles’ heel” means a vulnerable weakness, not a chain of released problems. “Crossing the Rubicon” means passing a point of no return, while “meeting one’s Waterloo” means suffering a decisive defeat. Those expressions come from different myths or historical traditions.