What English expression means an action that causes many previously hidden troubles to appear?

“Opening Pandora’s box” is the English expression for an action that causes many previously hidden troubles to appear. It comes from the myth in which Pandora opens a container and evils escape into the human world.

The expression is usually used metaphorically rather than literally. Someone may say that a decision “opened Pandora’s box” when it creates a chain of complicated, damaging, or difficult-to-control consequences. The phrase can apply to politics, technology, law, family disputes, or everyday choices.

The wording is based on a later version of the myth. Hesiod’s original Greek account describes a pithos, a large jar, not a box. Even so, “Pandora’s box” became the standard phrase in English and many other languages.

The expression differs from “opening the floodgates,” which means allowing a large amount of something to flow freely. “Opening Pandora’s box” specifically suggests that the consequences are harmful, unexpected, and difficult to reverse.