So there was this guy in the tower of London. He was a prisoner waiting to be executed. At his trial the judge said ""Your crimes are so heinous you'll be executed next week! But, I won't tell you which day because It'll be more terrifying if you are surprised."" As the prisoner was waiting in his cell, he figured: *They can't execute me on Sunday, because when Saturday night rolls around I'll know that there's only one day left for me to be executed, so I won't be surprised.* *By that logic, they couldn't execute me on Saturday either. Since I know it can't be Sunday on Friday night I'll know that I'll die tomorrow.* Following this train of thought, the prisoner realised that he couldn't be executed on any of the days next week if they wanted it to be a surprise. So he relaxed in his cell with the knowledge he was in no immediate danger, and when he was executed on Wednesday he was very surprised.