human relationship

Stuff happens.
We meet a lot of sorts people during our lives.
I know that they can't hurt me except definitely important person for me.
If the person who is definitely important and I have an emotional difference, I will get hurt.
Because the person can enter in my mind directly.
But just nasty people never can hurt my mind.
I think it is really difficult that someone hurt someone's mind. Only important person for them can hurt people's mind. Not important person never can hurt people's mind.

Is the person definitely important person for me?
If the answer is 'NO', it is unnecessary to be hurt.