Time. Time was a difficult thing to follow, moving differently as it did from realm to realm. To most of the souls down here, time meant very little. The world they'd left behind, the World Above, moved on as it would, and for some of them, a day equaled a lifetime above, as they reckoned it.
For others, the newer souls pouring in to Hades in waves of disappointment, heartbreak and anger, a minute above might seem like a lifetime here.
( Persephone straddled the line without any effort at all. )