The Shepherd Raised by the Wolf
A shepherd found a small abandoned wolf pup in the forest and brought it to his house. The shepherd fed the wolf pup with goat's milk, raised it, and trained it together with his own dogs. However, when the wolf grew up and matured, it began secretly strangling sheep at night and carrying them to wolves outside. Seeing the wolf caught red-handed, the shepherd banished it saying "I fed and raised you with my own hand, but I could not change the bloody rapacity inside you."
Creatures with evil, ferocity, and treachery in their disposition and lineage return to their own essence at the first opportunity no matter how well they are trained and fed. Education and upbringing are important, but not enough to completely destroy the bad nature coming from creation. Kindness done to dangerous and treacherous-natured people comes back to harm you one day. Creatures that do not forget their origin and lineage act as their own nature requires.
Rapacity of bad lineage does not completely change with training. Bad nature does not accept training. Kindness does not change a treacherous nature. Even if a wolf grows up, it acts like a wolf.
The traitor returning to their essence causes harm. The snake you feed bites one day. Not leaving precautions is essential.