I'm gonna out myself here: Anyone who thinks there are no such thing as ghosts has never encountered one!
I sometimes wish there weren't ghosts and I truly wish they were all Casper - cause some of them aren't so nice. Why are they here? Dunno. Why do they sometimes seem able to move stuff and others seem barely able to be seen - or heard? Dunno that either.
I was at a museum that had reenactors. I spoke to a man in civil war uniform for several minutes about his job. (They role play so I didn't find his speech or mannerisms odd.) I stuck my head out of the door to call my kids to speak to the man and when I turned around there was no one there. I looked back to see if there was another exit from the room, but it was solid rock all around. I asked the other staff who that was and I swear the guy went sheet white and started to stutter. They all looked at each other and asked me to wait a minute. A museum staffer came and asked me a ton of questions about the guy. Apparently I was not the only one to talk to this man, but I had a decent length conversation with him. The museum (no I won't name it here) still swears there was no one in that room.
That is the best documented, but I must be fairly sensitive because I got dozens of encounters, no dark stormy night things, no bloody heads stuff, just people who aren't there. It happens to my daughter sometimes too. She saw a woman in a house and later saw a painting of the woman who used to own the house and said she had seen her earlier in the day. She was four at the time.
BTW I see the little boy clearly but the other's look like reflections and distortions to me.....