Avatar: The Last Airbender fused its characterization with action to a marvelous degree, which meant many characters' unique abilities and skill sets were tied to their personality. At a pivotal moment, Zuko seeks to learn lightningbending but proves incapable, offering insight into the mechanics of how the subbending ability works. Even after that point, Zuko never demonstrates the ability to throw lightning bolts. What is it that stopped Zuko from lightningbending?
The Last Airbender first hinted at the ability for Firebenders to manipulate lightning in "The Storm," when Iroh redirected a lightning bolt that very nearly took out Zuko's ship. By Season 2, with the introduction of Zuko's sister Azula, it became clear that lightning was a valuable and rare ability whereby a Firebender released their energy into a deadly bolt of power. Iroh demonstrated that power as well, and during his journey with Zuko -- when both were on the lamb from the Fire Nation -- attempted to teach his nephew how to do it.
It failed miserably. Every time Zuko attempted to bend lightning, all he produced was an explosion that sent him back into the ground. Iroh explained that Zuko would never be able to master the skill as long as he struggled with his own inner conflict, which manifested itself in several ways as it progressed throughout Avatar. Instead, Zuko learned to redirect lightning using Iroh's own specially-crafted technique. He observed waterbending and utilized a careful control of the chi paths that sent electricity into one arm, through the gut rather than the heart, and out the other arm. Zuko employed this skill to great effect both against his father and Azula, eventually showing yet greater proficiency in the comics that continue past the show.
Yet at no point does Zuko ever demonstrate the ability to produce lightning himself -- even long after the resolution to the inner conflict Iroh identified as the reason he could not bend. That strikes some Avatar fans as curious, as they would assume Zuko's imminent talents allow him to master the ability that so many other Benders prove capable of. Azula is even able to redirect lightning herself by Smoke & Shadow, so what is it Zuko's sociopathic younger sister has that he doesn't?
The truth is that, for as resolved as Zuko's conflict may come to be during The Last Airbender, it never completely goes away. He defines himself by his struggles and conflicts, and indeed it's that process that makes his redemption arcs one of the best in modern television. Even after his first attempts to lightningbend, Zuko's inner conflict affected his abilities in various ways. Toward the end of the Book Two they made him so physically ill he could barely move, and after joining the Gaang in Book Three he had to go on a journey to rediscover a whole new emotional source to his firebending. Good or bad, Zuko is too temperamental to master the art of cool precision.
Azula, by contrast, has little difficulty in mastering her emotions. Even at her most manic in the finale, she proves capable of hurling lightning bolts. That speaks to the masterful ability to separate her mind and body, even in the midst of a psychotic break. Both Azula and Zuko are amazing characters in their own regard, but in analyzing and comparing them it is important to treat them on their own merits rather than reducing their abilities to a contest of action figures divorced from a personality.
As Zuko himself says, "I've always had to struggle and fight, and that's made me strong. It's made me who I am." Learning one of firebending's most powerful abilities just isn't right for the character, and it's why Avatar fans may never see the scarred Fire Lord throw lightning bolts of his own.
