What idiom is a fortune teller?

People who believe will answer "clever calculation"; The unbelieving answer is "nonsense" and "cheating".

In my opinion, I will answer with a story:

Once upon a time, three scholars went to Beijing to catch the exam. On the way, they met a fortune teller named "Living Immortal" and asked for advice: "How many can we take in this exam?" The fortune teller closed his eyes and counted for a while, then put up a finger. The three scholars didn't understand what it meant and asked for clarification. The fortune teller said, "The secret must not be revealed, and you will understand it later."

Later, only one of the three scholars was admitted, and that person came to reward him. As soon as they met, they praised him and said, "Sir, you are really good, and you really deserve your reputation." I also learned to put up a finger like a fortune teller and say, "There is really only one." After the scholar left, the fortune teller's wife asked him, "Why are you so smart?" The fortune teller smiled and said, "You don't understand the mystery. A finger can be erected to make a variety of explanations: if three people are admitted, it is' all admitted'; If you fail the exam, it is' all failed'; One in the exam is' one in the exam'; If you get two in the exam, it's' one failed'. No matter what the facts are, I can prove that my calculation is correct. "

Hearing this, the wife said happily, "You really have a set. I am convinced. "