Ghosts All humans have visits from those they knew in the past, now dead. These matters can be as simple as an apology they wished to express to you, or a bit of information they felt you needed, intended to be told to you when you next met.
Death interrupts the plans.
Ghosts are such disincarnate entities. Ghosts often show themselves to humans in a form that the human remembers. This is not a willful act on the part of the ghost, it is the way the human's mind perceives the ghost based on the fact that they understand they are communicating with someone they knew. The mind plays tricks where the human see what he expects to see or hopes to see, and fails to see something they do not wish to see. This is exactly what occurs when humans are being visited by ghosts.