What makes you you and not someone else, in Unamuno's sense? 

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juneamy007 eNotes educator| Certified Educator

“And the secret of human life, the universal secret, the root secret from which all other secrets spring, is the longing for more life, the furious and insatiable desire to be everything else without ever ceasing to be ourselves, to take possession of the entire universe without letting the universe take possession of us and absorb us; it is the desire to be someone else without ceasing to be myself, and continue being myself at the same time I am someone else...” 
― Miguel de Unamuno

According to Miguel de Unamuno embracing oneself is what makes you uniquely you and defines who you are in this world.  Once you set out to be someone else, then you have stopped being that which you were and continue on as a completely different being. 

“Those faults we do not have, do not bother us.” 
― Miguel de Unamuno

When we choose to embrace ourselves, faults and all; yet long to remove those same faults from others, we become ourselves and no one else.