Why are there so many reports of Ghosts?

For many many years there have been reports of ghosts, poltergeist activity and paranormal/supernatural stories that have taken place all over the world, yet none of it, as of yet been proven. I'm not disputing anyone who claims they have personally experienced it, as for them that is enough evidence and proof, but trying to convince others it was real is difficult from somebody with an objective point of view, skeptics.