There was once a scorpion who begged a frog to carry him across the river because he could not swim.

The frog hesitated for fearing being stung by the scorpion. The scorpion said: "Don't worry, you know I won't sting you since we will both drown if I do that". So the frog carried the scorpion across the river. But in the middle of the river, the scorpion stung the frog. The frog asked the scorpion in disbelief: "Why did you do this? Now we will both drown!" - "Because you are a game theorist and I am not!", replied the scorpion.