Avatar Course - Day 4 // Epic Narrative

"Reshape yourself through the power of your will; never let yourself be degraded by self-will. The will is the only friend of the Self, and the will is the only enemy of the Self. To those who have conquered themselves, the will is a friend. But it is the enemy of those who have not found the Self within them"

Bhagavad Gita, the Indian epic

Which Avatar character is this quote most relevant to?  Korra?  Zuko?  Someone else?