2. Elder brother to younger brother. There should be gentility in the elder brother and humility in the younger.
When Ozai was born, Iroh was already fifteen, with a life full of complications and obligations, so Ozai does not have many early members of his brother. And by the time Ozai was five, Iroh had married. Still, Ozai does remember some things, though he does not remember them often. He remembers that Iroh liked to pick him up and swing him around, that Iroh smiled often, that Iroh taught him his first firebending stance.
He also remembers that Iroh did not have much free time—he was always with tutors, trainers, and court officials. Iroh had even less free time after he married.
Ozai does not remember the wedding.
Ozai does not remember a time when he did not know that Iroh would become Fire Lord after their father, nor does he remember a time when Fire Lord Azulon's eyes did not sparkle with pride when he looked upon his eldest, and eventually, the eldest of his eldest: Lu Ten. Iroh inherits the same pride, and he looks upon Lu Ten in the same way.
It seems shameful to Ozai because this pride is folly. It continually clouds Azulon's judgment and Iroh's as well. Should not a father who expects his son to be a ruler show less favor, less mercy? Azulon's fondness for Iroh has made him soft, as Iroh's will do for Lu Ten. This baseless pride that stems from nothing but paternity is unseemly to the grandeur Ozai feels the Fire Lord should possess.
It is this pride that Ozai will learn to exploit, this love of sons, this weakness. It is a weakness Ozai will use against his father, his brother, but not himself: this love of sons that Ozai vows to never have.