"Remember the good times that we had? I let them slip away from us when things got bad How clearly I first saw you smilin' in the sun Wanna feel your warmth upon me, I wanna be the one
I will remember you Will you remember me? Don't let your life pass you by Weep not for the memories."
-Sarah McLachlan
He's a fully realized Avatar. He's stopped a century-long war without having to end a man's life. He's been hailed as the most powerful man in the world even though he's only thirteen years old.
But at the end of the day, Aang is still human and there are some things he cannot achieve. Like bringing people back from the dead.
It's getting dark, and he's exhausted from over a week of construction and rebuilding. Everyone else has gone to bed hours ago, but Aang won't be able to sleep until he's done. Wiping the sweat from his brow, he hangs the final tapestry and stands back to admire his...no, their work. He couldn't have done this without his friends, after all.
The Southern Air Temple has been restored to its former glory, but it's now a memorial shrine to a lost race and their culture. Perhaps somewhere in the back of his mind, the child in him thought this might revive his people from the dead. But Aang knows better.
"Well, Gyatso?" He smiles, tears blurring his vision. "I did it...no one will ever forget you or the Air Nomads now, I promise." The tapestry staring back at him says nothing; it's a perfect likeness of his mentor right down to the last laugh line, but the smile is nothing but paint and fabric.
Aang sits down before the tapestry, buries his face in his arms and cries.
He's the Avatar. He has power that rivals what the former Fire Lord had.
But at the end of ths day Aang is still human, and his pain is as real as anyone else's.