Can you read me like a book ?

I came to a theory tonight and it is:
That you never fully know someone.

Have you ever realized how you'll never know exactly what someone is thinking/feeling and therefore, as much as you THINK you know them.. you really don't. For instance, they could tell you they like something but really not or try to explain how they feel but sometimes words just can't express that.

So I guess my point is, the only person you'll ever fully know is yourself .. and truthfully, how well do we know ourselves ?!