How much people reveal about them

I was thinking about this and i was wondering how much people actually reveal some info to others which they may not want to share with everyone but their close ones. There may be some information which they do not even want to shares with anyone irrespective of how close any person is.
So if we classify personal information of an individual then there will be three categories.

1. Information which they do not mind sharing with anyone.
2. Information which they want to share with only close ones.
3. Information which they do not want to share with anyone.

Now different people may keep different information in different category. For example for a person A, information about his/her girl friend may be in category one but for some other person same info can be in some other category. It depends on the overall nature of the person. What might be the reason for a person to put something in a category and at the same time for any other person to put same thing in some other category. According to me this depends on the way an individual has been brought up. There may be several factors affecting this such as environment in which a person lives, his/her family background, family financial situation, social values etc.

There is another aspect of revealing info to others which is how i share info with others as described in the starting. Why is a person ready to share some info with someone but not with others. According to me the reason for this is that people have some fear in their mind or they are very possessive about something and that fear or possessiveness refrains them to share some info with everyone. For example, if i meet a strange person and i know that i am never going to meet that person again and if he/she asks me about something personal then i may not reveal actual info with him/her. Why did i not reveal exact info to that person even if i am not going to meet him/her again. This is because of the fear or possessiveness which i had. So everyone has some or other fear and everyone is possessive to some extent.