In Greek mythology, Pandora’s vessel left hope behind after the other troubles escaped. This is the familiar answer in modern retellings of the Pandora story.
Hesiod’s Works and Days says that the container held evils and that hope remained inside after Pandora replaced the lid. The passage has generated centuries of debate because it is not completely clear whether hope is meant as a comfort preserved for humanity or as another thing kept from humans.
Many popular versions simplify the story into a clear moral: even when suffering enters the world, hope remains. That interpretation is widespread, but readers should distinguish it from the more ambiguous wording of the ancient text.
The vessel is often called a box in English, although the ancient Greek object is usually understood as a large jar or storage container. The “box” wording became established through later translation and artistic tradition.