A scorpion asked a frog to take him across a river. The frog replied that he would not do it because the scorpion would sting him. The scorpion asked why would he have any reason to do that if they both had the same goal to get across the river. The frog agreed and let the scorpion on his back. Halfway across the river, the scorpion stung the frog. The frog, with his last breath asked why did he do that, because now they both will die.

The scorpion said, "because I'm a scorpion."