Seen from the corner of your eye… Perhaps something's real-er when you see it out of the corner of your eye. Because when you look head-on at something, you don't see everything. Take stars; have you ever been told to look sideways at stars? More importantly, have you ever done it? More stars are visible when you're looking just to the left/to the right/below/above the stars. It has to do with the cornea wearing out or becoming opaque or the photoreceptors at the center of the retina wearing out or something like that. Well, close enough.
Maybe that's why children can see ghosts and monsters and the like. Maybe when you see something out of the corner of your eye, it's real and what you see when you look is not.