It is what gets in the way of experiencing happiness; so when "it" is absent, happiness is experienced.
Ego is "that emotional and psychological knot in consciousness that is the fundamental cause of the sense of separation from all of life. From the spiritual perspective, this is defined as pride, self-importance, and the narcissistic need to always see oneself as being separate – separate from others, separate from the world, separate from the whole universe. Ego is a love-denying obsession with separation, narcissism, and self-concern." Andrew Cohen
Why do you need to "know yourself"?
read these on the internet... and i like what it says... :)