What does it take for people to turn on each other?

This question is vague.

Explanation:

While turning on people is considered rude and almost childish, there are many reasons as to why people do it. Many times a lack of trust in one another. Leaving the relationship destroyed and a lack of empathy is missing.

Or taking another approach, scientifically, a person can turn on another the same way an animal would. If a survival instinct were to kick in, any togetherness would be left behind and your mental state would turn selfish. Putting yourself first over helping others.