A friend of mine had this theory and I thought I'd share it with you. To put it simply, when Azula killed Aang at the end of Season 2 of 'The Last Airbender', and was subsequently brought back by Katara using the Spirit Oasis Water, the Avatar cycle was divided into twoseparatecycles, the physical, and the spiritual. Aang could still access the spiritual side of things, but he shared it with a Water tribe born at the moment he died by Azula's hand, who probably never truly realized his potential in his.her lifetime. By the time Korra was born, an Earth Kingdom Avatar had already been born with the Spiritual half, this was Amon. Tragedy twisted his destiny as the Avatar into using the Spiritual side of his power to seek balance tainted by the lust for vengeance. As to what the resolution of this could be, I cannot say, but in a weird way it makes a lot of sense.