"I can't help it, it's in my nature."
That was the reply from the scorpion to the frog, or a snake to a turtle depending upon the version of the fable being told, that gives a fatal lesson about innate nature.
As the story goes, a scorpion, or snake, needs to get to the other side of a river. The creature convinces a frog, or turtle, to carry him across after assuring no biting would take place because the poisonous venom would eventually kill both by putting each at the bottom of the river.
The end result is the snake, or scorpion, bites his floating companion simply because that's what they do. The animal doesn't know any better.
Which brings us to pit bulls. This breed was tailored by humans to be aggressive. Someone came up with the great idea of breeding this animal to fight and kill. They succeeded in their attempt, yet there are people who insist these animals can be good pets. The argument is that it's the owner who is at fault when a pit bull attacks another human or animal. We agree, but not completely. It's not the fault of the owner for not properly training the animal. It's the fault of the owner for simply having the animal.
Dogs can be great companions, but that particular breed has no place in a domestic setting.