There is no enemy…
"What?" Zuko gasped, flabbergasted. What his uncle had told him didn't make any sense.
Zuko had been stealing from the local Earth Kingdom village. Everyday he came back to their cave with more expensive items. Iroh knew that the reason Zuko felt he was justified in theft was because he still believed that the Earth Kingdom was their enemy. So the wise old man felt that Zuko needed to hear some advanced teachings, whether he was ready for them or not.
"There is no enemy, in this world or the next." Iroh sipped his tea, waiting to hear Zuko respond, but he heard nothing. Zuko sat patiently, waiting to hear why his Uncle would say something so odd.
"Well…" Iroh put his tea cup down. "…we are Fire Nation. The Avatar is our enemy. But from where he is standing, he is the hero and we are the enemy. The concept of 'hero' and 'enemy' are subjective terms. They are made-up, created by our own imaginations whenever struggle arises."
The Prince continued to listen.
"The only way someone can justify clearly evil acts is if they label the victim of those dark deeds as an enemy. Therefore, my nephew, that idea of labeling people as a true villain is unfair and foolish. For the Avatar is our enemy but only because we say he is. But if you were to take that label away from him, he'd just be a human being…like you and I."
Zuko looked at the ground and thought about what his Uncle had said. Iroh could see that he was carefully pondering his words, clashing them against what his own father had taught him.
A few moments later, the Prince stood up.
"You're a crazy old man." He said and left the cave.
Iroh sighed. He sensed that his nephew's frustration was only growing.