WHY?

I've done some thinking and the only question that got in my mind is WHY. Yep, why?

Why does a person hurt his/her friends?
Why does someone leave without a word?
Why are there insensitive, inconsiderate and self-centered people?
Why does one let go without a fight?
Why do we feel pain?
Why do people betray other people?
Why do some people prefer to suffer in silence?
Why do we cry?
Why can't we be angry with people who treated us with no respect?
Why do we have to be so understanding?
Why do you have vent out your anger on me?
Why did you do such a thing?
Why do you have to hurt me like that?

Been thinking about those since the other night and sadly, I couldn't answer them all by myself. I'm afraid some of these questions remain unanswered forever..