The Scorpion and the Frog is a fable about a scorpion and a frog who meet on the bank of a river. The scorpion asks the frog to carry him across the river on its back. The frog is afraid, because it knows that if the scorpion gets on its back, the scorpion could sting the frog and they will both drown. The scorpion says, "Don't worry, if I were to sting you, we would both drown!" The frog agrees and allows the scorpion to get on its back. When they are halfway across the river, the scorpion stings the frog and they both start to drown. As they are sinking, the frog asks the scorpion why it attacked it, even though it knew it would die too. The scorpion says, "It's in my nature."
The moral of this story is to not be fooled by what other people say when making decisions, because their actions may not be in line with their words. Even if someone promises something, you have to be aware of what they may do when they are in a tough situation.