Which English expression comes from the myth of Pandora opening her container?

The English expression that comes from the myth is “open Pandora’s box.”

To open Pandora’s box means to begin a chain of problems that may be difficult or impossible to stop. The expression derives from the later box version of the story, although Hesiod originally described a pithos, or large jar.

The idiom is usually used figuratively in journalism, politics, science, and everyday conversation. It does not necessarily mean that the person acted maliciously; it can describe an action whose unforeseen consequences create many new difficulties.

The phrase became established in English through the wider European reception of the myth. Its popularity helped make the box, rather than the original jar, the dominant image in modern retellings and explanations of the story.