Behavior of sociology? @_@

The study the behavior in connection to sociology, there a lot examples to initiate the word and its concept. Like, it is really strange to entertain strangers. I do have such experience, when someone called me through my mobile and asking somebody with different name. Then, all of a sudden they ask a lots of information. Automatically, I shut the conversations without giving information. I even think of having bad agenda towards me. That's really scary for someone to have the guts of doing so. Another example, Through experience, some other nationality has the wrong notion of someone. It is a stereotype behavior to scrutinize without considering the good things in them. It can also applied to some fellowmen, they acted like this to show their status in life. This will not change overnight, but hoping for the changes within them. What makes them like this?