Zuko is not good at lying to people and he is only good at acting when he's not stressed (and nothing about today is not stressful, he can't even count on his life not being in danger - he recalled troops two days ago and already there's been an assassination attempt), but one thing he's good at is lying to himself - that his father loves him, that a thirteen-year-old boy with no depth perception and a shaky grasp of firebending basics could capture and hold a hundred-and-eight-year-old Avatar, that it's better to side with his sister who always lies and go home than to stay with his uncle who had always tried to make home a person instead of a place -

That a sixteen-year-old who'd been banished twice could be Fire Lord.

It's actually lucky, in a way, that Katara hasn't been able to heal the lightning wound completely; Zuko lets the pain ground him in the here-and-now rather than the uncertain future, locks the truth of things away so he can't think about it and remember and then tells himself yes I can be Fire Lord, and puts on a smile for Aang, for the Fire Sages, for the whole multi-colored crowd that turned out for a teenaged boy's coronation; he won't let them see how scared he is.