Trying to decide which cup belongs to whom...
Lucas Meadows stashed this in Awkward Moments
Man in Black: All right. Where is the poison? The battle of wits has begun. It ends when you decide and we both drink, and find out who is right... and who is dead.
Vizzini: But it's so simple. All I have to do is divine from what I know of you: are you the sort of man who would put the poison into his own goblet or his enemy's? Now, a clever man would put the poison into his own goblet, because he would know that only a great fool would reach for what he was given. I am not a great fool, so I can clearly not choose the wine in front of you. But you must have known I was not a great fool, you would have counted on it, so I can clearly not choose the wine in front of me.
Man in Black: You've made your decision then?
Vizzini: Not remotely. Because iocane comes from Australia, as everyone knows, and Australia is entirely peopled with criminals, and criminals are used to having people not trust them, as you are not trusted by me, so I can clearly not choose the wine in front of you.
Man in Black: Truly, you have a dizzying intellect.
Vizzini: Wait till I get going! Now, where was I?
Man in Black: Australia.
Vizzini: Yes, Australia. And you must have suspected I would have known the powder's origin, so I can clearly not choose the wine in front of me.
Man in Black: You're just stalling now.
Vizzini: You'd like to think that, wouldn't you? You've beaten my giant, which means you're exceptionally strong, so you could've put the poison in your own goblet, trusting on your strength to save you, so I can clearly not choose the wine in front of you. But, you've also bested my Spaniard, which means you must have studied, and in studying you must have learned that man is mortal, so you would have put the poison as far from yourself as possible, so I can clearly not choose the wine in front of me.
Man in Black: You're trying to trick me into giving away something. It won't work.
Vizzini: IT HAS WORKED! YOU'VE GIVEN EVERYTHING AWAY! I KNOW WHERE THE POISON IS!
Man in Black: Then make your choice.
Vizzini: I will, and I choose - What in the world can that be?
Man in Black: [Vizzini gestures up and away from the table. Roberts looks. Vizzini swaps the goblets]
Man in Black: What? Where? I don't see anything.
Vizzini: Well, I- I could have sworn I saw something. No matter. First, let's drink. Me from my glass, and you from yours.
Man in Black, Vizzini: [Vizzini and the Man in Black drink]
Man in Black: You guessed wrong.
Vizzini: You only think I guessed wrong! That's what's so funny! I switched glasses when your back was turned! Ha ha! You fool! You fell victim to one of the classic blunders - The most famous of which is "never get involved in a land war in Asia" - but only slightly less well-known is this: "Never go against a Sicilian when death is on the line"! Ha ha ha ha ha ha ha! Ha ha ha ha ha ha ha! Ha ha ha...
Vizzini: [Vizzini stops suddenly, his smile frozen on his face and falls to the ground dead]
Buttercup: And to think, all that time it was your cup that was poisoned.
Man in Black: They were both poisoned. I spent the last few years building up an immunity to iocane powder.
This illustrates the concept of Common Knowledge in economic game theory:
"An item of information in a game is common knowledge if all of the players know it and all of the players know that all other players know it and all other players know that all other players know that all other players know it, and so on."
Dread Pirate Roberts exploits knowledge that is not common.
A lot of years ago I met the founder of Etch-it cups at an OC startup networking event (I think it was called Meet the VCs). Nobody was talking to him, so (despite everyone there talking at you) I went over and listened.
I asked him what he did, why he was here, why he was raising money, etc. He said he was looking for some operational cash to help with distribution to get marketspace at grocery supermarkets.
He pitched the Etch-it cup idea. I told him I thought it was interesting, but the real test is with my wife. He gave me a few and I took them home to "see if it would play in Peoria". My wife said it was the greatest thing ever. I passed her comments along and told him that he had a winning product and if there's anything I could ever do, I'd be happy to.
Next thing I know they were the hottest thing since sliced bread.
I love that story.