'Little Box of Horrors' isn't one of my favorite Charmed epidsodes. I think the writers screwed up the story of Pandora's Box a bit.
In the original myth, when Pandora was presented to Epimetheus, she opened the box. Doing this led to all the ills coming out, with hope left in the bottom of the box.
The 'Charmed' writers got all this right. Where I think they went wrong is the reason why hope was left in the box.
The ancient Greeks didn't like the idea of hope. They believed that whatever happened to you was because the gods wanted it to happen. There was no use in hoping against bad things happening because they would just happen anyway.
In this episode, though, Hope's friend assures her that "hope was the only thing left in the box, and that was what enabled the Greeks to put all the ills back in the box" (NOT a direct quote, by the way, so please don't sue me). In the myth, the ills never got put back in the box. This is where the writers got it all wrong.
I didn't like the other episodes ('Oh My Goddess 1 and 2') that use Greek mythology as a storyline. But more about that in my review for those episodes...