Why do some fortune tellers on the street know your last name through excessive fingers?

Actually, it's because you revealed it yourself. For example, he always asks you a few questions. If he doesn't ask you anything at all, just like the one upstairs said he knew you. There is also a very simple one. He found some pieces of paper with various surnames on it to show you whether this one has many surnames. In fact, according to the probability, you will know which one it is after you point it out two or three times, but he can't remember it at all, so he knows your last name. In short, it is all kinds of deceptive tricks.