In Greek mythology, hope remained in Pandora’s jar after she opened it. The familiar version says that harmful forces escaped into the world, while hope stayed behind when the container was closed.
The detail comes from the tradition surrounding Hesiod’s Pandora story, although the exact interpretation of hope has been debated. Some readers see hope as a comfort preserved for humanity; others note that the Greek word elpis can have a broader meaning than modern optimism.
This question is distinct from asking what escaped from the container. In the best-known modern retelling, the answer to that question is evils or miseries, while hope is the notable thing associated with remaining inside. The ancient text’s wording and the container’s identity have both generated scholarly discussion.