In Aristotle's Poetics.

In his Poetics, Aristotle outlined the ingredients necessary for a good tragedy, and he based his formula on what he considered to be the perfect tragedy, Sophocles's Oedipus the King. According to Aristotle, a tragedy must be an imitation of life in the form of a serious story that is complete in itself; in other words, the story must be realistic and narrow in focus. A good tragedy will evoke pity and fear in its …

…emselves, a man who is great but not perfect, who is a good father, husband, and son, and yet who unwillingly destroys parents, wife and children. Oedipus is human, regardless of his pride, his intelligence, or his stubbornness, and we recognize this in his agonizing reaction to his sin. Watching this, the audience is certainly moved to both pity and fear: pity for this broken man, and fear that his tragedy could be our own.