That presupposes that gjosts are sentient, rather than recordings or telepathic transmissions or dimensional anomalies or whatever (see Vizh's list of hypotheses). I think there's rather less evidence for sentience in ghosts (excluding poltergeists) than for the occasional appearance of apparitions. There's very few accounts of ghosts actually doing a Hamlet's father or revealing the buried treasure etc.

That said I love the story of the Cock Lane Ghost, a very old genuine English court case in which a man was tried for the murder of his vanished wife based upon the alleged haunting perceived by his next door neighbours in which the woman accused her husband of her death. Google the details sometime.




That also accounts for the lack of death wounds on most ghosts (except the headless ones), and might explain why most ghosts are perceived repeating actions they did in life.




The next logical step to that argument is that the ghost doesn't need to be the person at all, just a phenomenon that the human mind assigns an expected shape or form to; and that in turn opens up possibilities of explaining UFOs, fairies, and the blessed virgin Mary.