Someone once encountered and captured a relatively tame and docile forest animal. The person was, however, very sadistic. Despite initial kindness to win the animal over, over time this kindness changed. When the animal didn't do exactly what the person wanted, this person treated the animal badly.
This went on for many years. The animal cooperated for a long time, for the most part, because it came to be dependent on the human. But it finally desired to be free of it's cage. It had times when it got to experience a different life, brief moments where it finally saw what true happiness could be.
Eventually the animal was pushed far enough that it left. But in the process of leaving, the human, after first opening the doors for the animal, lashed out in it's anger over the animal leaving.
It was one time too many. The animal, for the most part tame, was driven back to it's untamed instincts. It lashed out in response, it's anger and hurt too much for it to keep inside any longer.
But at it’s core, it still was not cruel or malicious. It only desired freedom from the human who initially had shown it kindness, but for so long had treated the animal like a piece of property…like something to do tricks to amuse them.
They parted ways. But both were harmed in the process…permanently harmed. The human became bitter and petty, rejecting all creatures like the one they felt had wronged them. The animal harbored a deep mistrust and fear of humans, and developed a new instinct…instinctive hatred of the human and all that were like that human.