But how self-focused is self-knowledge? Paradoxically, self-knowledge cannot be gained but through others. Thus in Plato, one’s beloved supplies a window into the self, the self one sees mirrored in the adoring looks of one’s beloved. But that only underscores the paradox of self-knowledge, which is never simply knowledge of the self, but of the self in relation to others.
— Andrew Schultz
The Floating Library 
You are so right when you said “the paradox of self-knowledge, which is never simply knowledge of the self, but of the self in relation to others.” “self” can only exist when it is measured against others, otherwise it is only an abstract thought. “self” can only be expresed thru one’s actions. There is a new book out that takes Platos position one step further the book is called The Power of Self Seperation Acceptance or Rejection. You will enjoy reading it.