I forget where I read an article about this being the reason people see ghosts in passing while panicked. Your brain making you see shadows as people walking or faces so you stay alert.
Was kicking it about this once on the topic of
Shadow People and how they are only ever seen out of the periphery of your vision. They were adamant they exist whereas I said the sides of our eyes are meant to detect motion, not detail. Add that in with stress and expectation and it is what it is.
Its like how people walking out at night in the dark may see a coiled rope and think it was a snake until they get a closer glimpse but a lot of these erroneous assumptions are placed in their heads back when and run unchecked for their time on the planet. The implications of that are quite something because, in one sense, if enough people believe an illusion it came seem self evident to the rest who buy in until reappraised with the eyes of Inner Sense.
Just like the Emperor who was actually naked but people manufactured proof as they lied to themselves. All in all this is a fascinating thread though because whilst the Mandela premise doesn't hold much sway with me I do know a bit about memory and its flex as well as the various "camera tricks" in our head along with immense chunks of editing.