Those who have seen the 1992 flick The Crying Game may remember the story that Jody tells Fergus in the context of good and bad people, the story being a metaphor for the movie as a whole:
Scorpion wants to cross a river, but he can't swim. Goes to the frog, who can, and asks for a ride. Frog says, "If I give you a ride on my back, you'll go and sting me." Scorpion replies, "It would not be in my interest to sting you since as I'll be on your back we both would drown." Frog thinks about this logic for a while and accepts the deal. Takes the scorpion on his back. Braves the waters. Halfway over feels a burning spear in his side and realizes the scorpion has stung him after all. And as they both sink beneath the waves the frog cries out, "Why did you sting me, Mr. Scorpion, for now we both will drown?" Scorpion replies, "I can't help it, it's in my nature."
See it at: http://www.youtube.com/watch?v=M0I44-XPk2A
The meaning of the story is clear: creatures (including people) will remain true to their natures, irrespective of external influences. The frog takes the scorpion at its word and agrees to transport the scorpion, notwithstanding that there is nothing in it for the frog. The scorpion on the other hand will remain true to its dangerous innate nature, even though it is treated with trust and kindness.
