When looking at the concept of human nature I like to turn to a man who seemed to have this figured out entirly. Socrates:
True to his teaching that "an unexamined life is not worth living", Socrates spent most of his days examining the real reasons, or motivation, behind his human acts . His final act, in fact, epitomized what he was all about: Falsely sentenced to death for corrupting the youth and not believing in the ancestral gods, Socrates, rather than suffer exile from the Athens he loved so much, willingly and with his own hand ended his life with a drink of deadly hemlock. Plato and Xenophon, Socrates' main biographers, paint his vocation, or calling in life, as an ardent desire to help people to live life to the fullest; that is, to live in conformity with their human nature.
In an ancient account of philosophy there are three parts; ethics, physics, and dialectic or logic. Everyday Socrates examined his life and the life around him... Socrates used to say that we should never lead a life not subjected to examination.
The "unexamined life" i.e. the life lived in disobedience to the exhortation "know thy self", is the opposite of the life Socrates tried to live, and in that sense 'I know' = 'I have learned' or 'I have discovered' that I am without wisdom. Socrates knew that he was without wisdom because he had questioned [examined] himself and questioned [examined] all others he could find who were said to be wise, and nowhere did he find the wisdom that he has sought, 'wisdom' meaning here: knowledge of the correct way for a human being to live, knowledge of the particular excellence that is appropriate to human nature.
Thus Socrates introduced the ethics part of philosophy and this makes me wonder that if we as people do not question our selves and live the life of human excellence that we beleive to be exceptable after questioning ones self, are we living a "fullfilled life"? If we do not examine our lives and better them, then are our lives worth living?