Why do poeple bully others?

I think that there are two reasons why someone would bully another person. The first reason is because they get a reaction. If one is being bullied and they get upset then then the bully will just continue to bully that person. But if someone is being bullied and shows no reaction the bully will get bored. The second reason that I think someone would bully another person is because the person they're bullying is someone that nobody likes, it makes it seem like it's not as bad because everyone is bullying that person. But that is definitely not true.