Now darken the room except for a single lit candle, stare into the mirror and say “Candyman” three times.
That’s the stupidest thing I’ve ever heard! Everybody knows you say, “I believe in Mary Worth” three times!
lol. I thought of Mary Worth, too; and then I thought, no that was a comic strip...

...but there are different theories on how that began covered in this article.
The real trick is covered in the 2nd video where the hippie guy explains how light bounces off every surface geometrically like the billiard ball example someone cited, but he didn't cover how our eyes and brain "read" and process that in a way we can comprehend.
For a while I studied holography with the intention of helping perfect the medium but the concepts, logical in written form, made no sense to my mind in physical reality - at times inducing headaches so I gave it up. Rather shameful for a guy whose father was a professional magician.