Which Avatar Made the Biggest Mistake in Avatar: The Last Airbender?

Avatar: The Last Airbender and The Legend of Korra are centered around the Avatar, a mantle passed from one brave bender to another, all of whom must save the world as a fighter and diplomat. Being the Avatar is never easy, as Avatar Aang himself soon realized, and even the ultimate bender sometimes makes a blunder with enormous consequences. Since they’re only human, and because the cartoon’s narrative needs conflict, the Avatars are known equally for their mistakes and their successes.