Why are some people not nice and sometimes evil?

I keep meeting people who are just not kind or are on complete opposite wavelengths than me. I met this girl recently who I thought I could be friends with and it turns out she was so strange and not kind when I met her the second time. She made me feel super uncomfortable and upset by some of her actions.

I just wonder why not so nice people exist and why sometimes we encounter such different people than us in life. What would Jung’s take be on it? I don’t think being nice is relative, some people are just not kind and are more secretive and closed off and create a lot of discomfort for others and I just wonder why they are that way and why they exist.