In the wake of the new Star Trek movie, I've been watching some of the old series episodes, available through CBS' website. Yesterday I saw "The Enemy Within", where a transporter accident causes Kirk to split into a "good Kirk" and "bad Kirk".
Well, they start out talking about the good Kirk and bad Kirk, but further qualify it as the intellect vs. the emotions, or perhaps the superego vs. the id. Neither side can exist long-term without the other. The intellectual, compassionate side cannot command a starship without the drive, the ambition, the will to do what must be done even if it will cause pain or difficulty. Much of the show is devoted to showing the two sides, and trying to find a way to reintegrate them before the two split halves die.
Debbie sees it as the Yetzer haTov (will to do good for others) and the Yetzer ha-Ra, (will to do evil by gratifying selfish urges) both of which are necessary for a person to live. She further believes that all have an exact balance of Yetzer haTov and Yetzer ha-Ra. We talk of one yetzer or another being stronger, but if you look at the totality of Jewish literature, it seems that the two are in exact balance. Those who are great personalities, such as Yaakov or David or Shlomo, certainly have great Yetzer haTov, given how they live their lives devoted to greatness in God's name. However, they all are tested by an equally huge Yetzer ha-Ra.
David, with Batsheva, Shlomo with his wives and idolatry, Yaakov with Lavan and Esav, and all are found wanting in Rabbinic literature in the way they meet these challenges. While we are to say that "they did not sin", still, as David told his prophet Nathan, their actions are not uncensured or uncensurable. David did not technically sin, but he was greatly tempted and gave in to temptation.
Yaakov in dealing with Esav has to descend to trickery to ensure he gets the proper blessing, but is in turn tricked by Lavan repeatedly, and his life is made miserable as he is tricked by Lavan, tricked by his children, etc. He was blessed in that all his children, unlike his father and grandfather before him, went in the way of Torah - he was the only sole father of our nation. But he was also punished for his negative acts.
If one is granted a great Yetzer ha-Tov, internal drive to do good, one is also tested by a massive Yetzer-haRa, internal drive to slip up, do the wrong thing. In this, as in many things, there is and must be a perfect balance for the person to be a true servant of God, to have the power to choose rightly, and be rewarded by greatness, even if that is accompanied by the power to choose wrongly.
(updated: changed translation of YhT and YhR)