Why do some people become kinder after experiencing hardship, while others become bitter?

What are the dangers of being unaware of how ideas and beliefs can be implanted in our minds, as suggested by the concept of soul theft?
What is it about narcissists that makes them always have a "dead to me" list of former friends or close ones?
Why would a silverback gorilla give you a chance to back off, while a polar bear wouldn’t in a hypothetical fight scenario?