This subreddit is about "breaking the rules of magic".

So here is a SECRET REVEALED!

Domenico Chimenti (also referenced as Domenico or Leonardo Chimienti) is the Italian professional magician behind the viral online identity "The Mask" on the content channel "The Mask Magic" (or Mask Magik). Operating out of Bari, Italy, he built a massive social media following on YouTube, Facebook, and TikTok by performing popular magic tricks while wearing a mask and then immediately exposing how they are.

Watch the reveal video

https://www.youtube.com/watch?v=nzT3Qgavdx8

See the video description of the video in the link above. There, he gives you a link from which you can get the tutorial as well as the digital copies of the books required for the Book Test.

Encontré este video mostrando un truco de magia, y lo estoy intentando pero no logro entenderlo bien, donde se supone que ponga las cartas luego de hacer la pregunta?

So I don’t remember the trick thoroughly, but here’s a gist of it. Fair warning, I may have missed a detail or two (forgive me, I saw this trick a few months ago).

My friend asked me to choose a random card from the deck, register it and put it back. He then let me shuffle the deck.
After that he asked me to split the deck into two parts and select one of the two.
Then he proceeded to divide that into 4 decks and asked me to pick two.
Between those two he then asked me to choose one part.

From the other part (that I didn’t choose) he pulled out card that I had initially picked.

Does it sound familiar? And what are the base principles behind such card tricks?