In Greek mythology, hope was the one thing left inside Pandora’s container.
According to Hesiod’s Works and Days, Pandora opened a large storage jar, releasing the troubles that had previously been kept away from humanity. The text says that only Elpis, commonly translated as “Hope,” remained inside after Pandora closed the lid. The precise meaning of Elpis has been debated because ancient Greek hope could refer to expectation generally, not only optimism.
Later retellings usually present Hope as a comfort deliberately preserved for humankind. Some interpretations instead ask whether Hope was another evil held back in the jar, but that is an interpretation rather than an explicit conclusion in Hesiod’s brief account. The familiar phrase “Pandora’s box” arose because Erasmus translated the Greek word for jar as a Latin term meaning box.
Hope is therefore the standard canonical answer, although discussions of the myth often focus on the ambiguity of why it remained inside.