"Perception is reality."
This is why I always try to stay in people's peripheral vision. Am I real? Am I a ghost? Who knows. My existence is independent of your observed reality, but as long as I am partially existing within that observable reality I'm going to mess with you.
But it's important that if you are in a relationship, cut off all contact with anyone who might be a potential cheating candidate. Hot single friends? Got to go. Recent divorcees on the rebound? Get 'em outta there.
Old Mrs. Haberdasher, the 86 year old widow who lives down the road? Careful. She was a man eater back in her heyday. She's waiting for her opportunity to pounce.