Even after normal people die, they may not realize they are dead. They often believe they are still alive, though their thoughts can be somewhat muddled, not too clear-headed.
If someone is hastily buried before their soul figures it out, and they see themselves being buried alive, naturally, they will be filled with resentment, enduring the burning pain of soul and flesh, transforming into a fierce ghost.
The reason for keeping vigil over the deceased comes from this principle. A person may not know they've died, but seeing a large group of distant relatives, whom they've never met, eagerly coming to feast, they'll understand someone must have died.
Why is that person themself?
The deceased then comes to a sudden realization, "Oh, so this crowd of people is here to feast on me."
