S2E9 · Book Two: Earth - Chapter Nine: Bitter Work

Complete story — includes the ending

Aang begins his earthbending training with Toph, but grows frustrated when he encounters difficulty with earth, the natural opposite of air. Aang's inclination towards agility and evasion puts him at a disadvantage with earthbending, which requires a more direct, resolute form of combat. Elsewhere, Zuko struggles with a similar dilemma as Iroh tries to teach him lightning-bending, an advanced form of firebending; Zuko's anger keeps him from having the cold precision lightning-bending requires. When Sokka is endangered by a saber-toothed Moose-Lion, Aang is able to save him by firmly standing his ground as an earthbender would, leading to his first successful try at earthbending. After being taught by Iroh the significance of drawing wisdom from all four nations, much like the Avatar, Zuko claims he's ready to try and re-direct real lightning, a technique Iroh invented by studying the waterbenders. Iroh staunchly refuses, with Zuko resorting to standing on a mountaintop during a storm while tearfully screaming at the heavens to strike him like they have in the past.