answered on 5 Jun 2019:
last edited 6 Jun 2019 6:04 am
Hmmm… have you ever heard of the saying “hurt people are the ones who hurt people”? This saying is to say that when people are hurting, they will then in turn hurt others. So: I think that people can become bad hearted when they are hurting or sad and so then to them, hurting other people is the only thing that they know how to do.
As for why some people are kind, it could be that they just have joy in their heart, or maybe they ascribe to a religion or worldview that helps them see joy in the world, and helps them to cultivate love and kindness.