What modern idiom describes an action that creates many new problems, like opening Pandora’s box?

The modern idiom for an action that creates many new problems, like opening Pandora’s box, is “open a can of worms.”

The expression means to create a complicated situation by trying to deal with one issue. Once opened, a can of worms suggests a mess that is difficult to contain or resolve. It is therefore used as a modern metaphor with a meaning similar to the consequences associated with Pandora’s vessel.

“Open Pandora’s box” is itself an idiom meaning to start a chain of unforeseen troubles. The two expressions are related in meaning but are not the same phrase. A question asking for the parallel idiom must therefore distinguish the can-of-worms expression from other common idioms about difficulty or action.

The exact origin of “can of worms” is uncertain, and the phrase became widespread in twentieth-century English. Its imagery is modern, whereas the Pandora story comes from ancient Greek literature.