Azula was able to do it because Aang was vulnerable for a split second while activating the Avatar State, and she landed a lightning strike before he could fully settle into it. The scene also matters because Aang had just been focused on chakra/Avatar State control, so he wasn’t in a steady combat posture yet.

What happened

Aang was rising into the Avatar State when Azula attacked from a favorable angle and hit him with lightning in the back. That timing is the key reason it worked: she didn’t overpower the Avatar State head-on so much as catch him during the transition.

Why it worked

  • Azula is an elite firebender and lightning user, so her attack was fast and precise.
  • Aang was distracted and not fully in control at that moment.
  • The Avatar State does not make him instantly untouchable in every frame of motion; timing still matters.

Story logic

In-universe, the moment is meant to show that Azula is extremely dangerous, especially when she gets the first clean shot. It also shows that even the Avatar can be caught off guard when the opponent is disciplined, ruthless, and perfectly timed.

TL;DR

Azula didn’t beat the Avatar State by brute force; she landed a lightning strike at the exact moment Aang was exposed, before he could fully control the state.