Who knows us best? Not ourselves. For you to truly know who you are, you'd have to stand at the end of your life and review everything you ever did. Look at how you acted, and how your actions affected others. Listen to what you said, and find out how others heard you. Dive into your own thoughts, and analyze how these affected how you acted, and how you spoke.
And them? Do they know you? To some extent, of course. But most of who you are, and what you are, is lost in your attempt to be.
To be what? What are you trying to be? And more importantly, were you successful in being? You were trying to be what you thought you should be, and what you thought people thought you should be. In the process, you realized that you should stop trying and just let yourself be.
And then you ask yourself again: Who am I?
So you go through life, attempting to figure out who you are. When you get to the end, you still haven't figured out who you are. So you review everything you ever did.