What is the modern idiom “open Pandora’s box” used to describe?

The modern idiom “open Pandora’s box” means starting many unforeseen problems.

The expression comes from the Greek myth in which Pandora opens a sealed vessel and releases troubles into the world. In modern English, it describes an action that appears limited or manageable but produces a cascade of complicated, harmful, or difficult consequences.

The idiom is often used in journalism, politics, law, science, and everyday conversation. For example, a new policy may be said to open Pandora’s box if it creates disputes or consequences that were not anticipated. The phrase does not usually refer to a literal container.

The wording also preserves a translation history. Hesiod described a pithos, or large jar, while later Latin and European traditions popularized “box.” The idiom therefore combines an ancient Greek story with a later linguistic transformation.