Disclaiming Banner: Allow me to state that I have more chances of splitting a boulder with my head than making money from fanfiction.
Secret
Iroh didn't just play his tiles close to the vest. He might as well have carried them in his bones. Some of his secrets could have whole clans wiped out for high treason. Others would send what was left of his people scrabbling into chaos.
One of the lesser, (but no less stringently guarded mysteries) was the day that he turned against his father. Now some would consider his son's death to be the cause. It was in fact, the day his son was born that he turned in his heart from Azulon. The wife that had been chosen for him lay in danger from the exertions of childbirth and the Firelord would not deign to see the infant.
He was too busy organizing the invasion of the Hu Xin Provinces in the Earth Kingdom just across the courtyard.