Why I don't like to share (what's going on in my life) anything with anyone.

I am 25 Male, I have been looking for these answer so long but unable to find out so i decided to create a thread. Ok here is the thing, since my childhood I don't like to share anything what's going on in my life neither good nor bad to any one including parents. If anyone ask me about my life I just brush it off just saying I am fine and then I turned the entire conversation and let him/her speak about himself/herself. I have been doing these since my childhood and now I am wondering whether am i being selfish for not sharing thing with those people. Its not like I don't trust them or anything it is unable to explain in words TBH. I have had read some post in the reddit, people do these kind of staff because of past experiences but I have never been through anything in my life. If any one have any advices for me kindly don't hesitate to share. Thanks.