Theory: Ghosts are (what's left of) a person's daimon

[Omegaphallic]

Geist 2e has heavily refocused the metaphysics to the point that the Underworld is arguably the most hostile otherworld of the common set. It's always been right upstairs from the Lower Depths in conventional maps of the cosmology, and 2e makes that very plain; the Shadow is made of things that want to eat the locals and the Hedge actively attempts to trap you, but the Underworld does both of those things at the same time.

There's a post by Dave Brookshaw on these forums that describes the Underworld as "provably the worst-damaged [part of the] Fallen World" and it's very hard to disagree with that assessment when looking at what the Underworld does to ghosts.

It also suffers from resource scarcity in a way the Hedge, Shadow, and Astral doesn't, Ghosts in the Underworld struggle hard for resources, especially in the upper regions, and running out of Essence is a horrifying way for a Ghost to go down.

Also the Spirits of the Shadow might hunt each other, but only within certain rules, and the Shadow itself does not try and kill and eat you, it's inhabitant do.

Same with the Hedge and Astral Plane (which depending on the location is the safest of the Realms), but with the Underworld, your Ghost is food, your lunch, the Underworld is the biggest predator of all, but not the only one, and the best you can do to bribe it to leave you allow with essence or hide in the Domains till it eats that Domain.