Do they know you or do you know them too much?

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A few days I suddenly realised this theory.. it's been drifting in my mind..
People who love to talk to you a lot about themselves actually don't know much about you in some aspects.
I have a few friends like that.. they often give me things that they think is my style.. but in actual fact.. it is the opposite... and I think i tell them that.. but they don't seem to remember... or maybe i just look like a stereotypical sort of person such that they will always see me in that light and put me in that box...
same goes for me and some other people.. i can see that for myself.. those people i talk to a lot.. i know less about their certain aspects than they know about me...
interesting isn't it.. is there such a thing as a balanced friendship?