There was a scorpion trying to get across a pond, but didn't swim and so it wouldn't dare to get in the water. A few moments later a frog showed up on shore and asked the scorpion what it was doing, the Scorpion replied that it was simply looking to get across the pond, and seeing that the frog was a great swimmer asked the frog to let him ride on her back, that way he'd be able to get across the pond.
The frog refused, saying that if he were to allow the scorpion to climb on his back, the scorpion would eventually sting him and then he'd be dead. The scorpion rebutted by saying that he would never do that, as he would drown himself, and why would he ever hurt someone who's helping him. He promised and promised and they negotiated until the frog agreed to help him.
The scorpion climbed on the back of the frog and they took off across the pond, halfway through the pond the scorpion stung the frog and she started to sink, the scorpion followed right behind. One their way down the frog asked the scorpion why he had done it, now they'd both die, and the scorpion simply replied that he could not go against his nature.