You see, the frog and the scorpion aren't actually real.
They were just characters in a story.
The author of this story had no clue that this simple tale of a frog and a scorpion would be interpreted as a deep metaphor on human behavior by all who read it.
The scorpion isn't a metaphor for selfishness. The frog isn't a metaphor for trust.
They're just animals.
There was no deep meaning, no lesson to be taught.
They weren't even real.