system
Given the following post, respond as if you're commenting on Reddit:
human
[general horror] Why do ghosts spend so much time moving random objects, walking across halls in the background, grabbing shoulders from behind, and playing piano?

Ghosts used to be living people. Yet, they behave very unlike living people. They're always walking loudly on wooden steps, hiding in closets and drawers like weirdos, jumping out from the dark at people, pointlessly turning on or off lights, moving things around for no reason, walking behind people ominously, playing sad off-key tunes on the piano, grabbing shoulders, leaving ectoplasm everywhere, and generally making a nuisance of themselves. They always seem to whisper and leave needlessly cryptic messages instead of just saying what they want outright.

Why is it that after they die they start acting so-- oddly? Why not fly aroundand explore galaxies and other dimensions and stuff? Do they really have to be such crummy roommates?
gpt
Alejandro Amenábar's movie The Others offered a pretty interesting explanation for this, which was that ghosts might not realize they are even dead, and are just going through their daily lives in a plane of existence parallel to the living. 

All the weird stuff people in the realm of the living experience are generally mundane actions the ghosts are doing, but bleeding into our world (voices from nowhere, doors randomly opening, a piano playing itself, or objects being moved around).

And the bleeding can go the other way too, with actions happening in the living plane bleeding into the dead's plane. 

But if the ghosts still think themselves to be alive, they mistake the living for the ghosts, and end up behaving like they're the ones being haunted, panic and flip out, which creates even crazier actions bleeding back into the plane of the living, and a reciprocating cycle where both planes are unintentionally freaking each other out.

Once the ghosts realize and accept that they're dead though, they can finally calm down and be more like benevolent or passive spirits if they wanted to.