Why do people behave the way they do in their daily lives?

In order to to answer this overall research question, I will try to find out:

1. Why people bully and tease others?
2.  What causes people to feel certain emotions?

I already know that sometimes people bully others because of their own insecurities, and I also know that certain chemicals in the brain create sensations of each emotion, but I still want to know what causes those chemicals and I want to go into more depth with why exactly people bully.