Why does your stomach hurt when you are anxious? Is it a random thing? Why is a person stressed/anxious when he thinks too much about future? Why does a liar feel guilty? Why does a person who has extramarital sex cannot face his spouse? Why does a murderer feel guilty about his actions? He could have felt happy about doing these misdeeds...but no.
Is this randomness...i(sorry i mean Buddha and many intelligent people) say there is a cause for everything that happens. It's the laws of nature to hurt a person that hurts others....someone, somewhere will give it back to him/her.
I don't mean to say Social phobics are bad people....but i do believe somewhere i am the creator of my present. If i can be good now...my future will be brighter and happier. That's my whole point.