|“||Elpis, the Spirit of Hope, would not abandon humanity. Hope does not leave without being given permission. She can only be released by a child of man.||”|
After Prometheus gave fire to humans, Elpis was placed by Zeus in Pandora's Pithos, along evil spirits. When Pandora opened the jar and its contents were unleashed onto the world, Elpis was the only remaining benevolent spirit, staying with humanity so they wouldn't give up hope.
When Prometheus was enlisted to organize a truce between the demigods and Titans for a peaceful end to the fighting, he had Pandora's Pithos in his possession. When Percy Jackson refused, Prometheus gave him the jar so that when he was ready to surrender, all he had to do was release her, symbolically "giving up hope."
Though Percy was tempted to throughout the entire battle, Elpis was never released. In the end, he gave her to Hestia for safekeeping because "hope survives best at the hearth." Hestia has since retained guardianship of the pithos.
- Percy speculates that Zeus had some sense of shame by having Elpis be the sole good spirit amongst the evil ones in Pandora's Pithos. 
- Percy Jackson's Greek Gods, You Gotta Love Aphrodite