It was humiliating. Being told to battle his father.
He felt so stupid; not realizing it was him he'd have to fight. His own father, fighting him in a duel to the death. He hated himself for a moment, realizing that Ozai did not care. But he could try! Yes, try to convince his father to stop this… humiliation and forgive him.
He fell to his knees. "Please, Father! I only had the Fire Nation's best interest at heart! I'm sorry I spoke out of turn!"
Ozai approached him. "You will fight for your honor."
"I meant you no disrespect!" Zuko protested. "I am your loyal son!"
Ozai shook his head. "You will learn respect, and suffering will be your teacher." Uncle looked away, but Azula smirked. The cruel little brat. Ozai raised his hand. Zuko screeched. It hurt! It hurt so much. It hurt him physically and mentally. His pride, his honor, his family—he knew they were all gone. "You have shown shameful weakness," his father declared. "You are banished. You may only return if you capture the Avatar. Only then will you regain your honor."
But forever, Zuko would be publically shamed. The public humiliation only ended when he joined the Avatar—when he did exactly the opposite of what his father commanded. And then, he found, his honor relied on himself, not Ozai.