It’s one of my favorite paradoxes.
A man is sentenced to death.
The judge says, “You will be executed the following week between Monday and Friday. It will be a surprise to you.”
The condemned man goes back to his cell and thinks about what the judge said.
He deduces that if he isn’t executed by end of day Thursday, he won’t be executed on Friday, because it would no longer be a surprise to him.
He then realizes, “If they haven’t executed me by end of day Wednesday, it can’t happen on a Thursday either, because Friday is already not possible. And with no other options, it wouldn’t be a surprise if they executed me on Thursday either.”
He works back from this line of reasoning, and concludes that he won’t actually be executed the following week.
Then, he’s shocked when the executioner knocks on his door on Wednesday at noon.
And because he was surprised, the judge was still proven correct.
Like many paradoxes, it’s a word game.
The prisoner didn’t realize that, no matter how much he plays games with semantics, or how much he convinces himself it won’t happen—he will be executed the following week.
It’s akin to convincing yourself you can win a random-chance game of slot machines because you are smart.