What modern expression comes from Pandora opening the mythological jar?

The modern expression is “opening Pandora’s box.”

It describes starting an action or investigation that produces many unexpected problems. The phrase comes from the myth in which Pandora opens a container and releases the world’s troubles. Although the ancient story involved a jar, the box wording became standard through later translation and popular retelling.

The expression is normally used metaphorically rather than literally. Someone may say that a government inquiry, a technological invention, or a difficult question “opened Pandora’s box” when it created consequences that could not easily be controlled.

The phrase is related to, but distinct from, other myth-based expressions. “Achilles’ heel” means a vulnerable point, “Midas touch” suggests unusual success, and “crossing the Rubicon” refers to an irreversible decision. “Opening Pandora’s box” specifically emphasizes unforeseen troubles released by one action.