Question: A thief enters a shop and threatens the clerk, forcing him to open the safe. The clerk says, "The code for the safe is different every day, and if you hurt me you'll never get the code". But the thief manages to guess the code on his own.
How did he do it?
Answer: The code is "different." The clerk told him this.
Question: When you talk about it, it disappears. What is it? A. A secret B. Silence C. Time
Answer: A and B. If you talk about silence then it's not silent anymore. If you talk about a secret, then other people know about it so it's not a secret anymore.