system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar/legend of korra] if bending is only a manipulation of the elements rather than generating said elements how do fire benders use their powers when there is no source of fire to draw upon?
gpt
Firebenders do need their element to be present, but they thing they manipulate isn't just fire, it's actually *heat*, fire is just the most basic way they manifest it. The sun acts as a constant and powerful, albeit distant, source of heat. This is why they are less powerful at night, and lose their powers completely during a solar eclipse. Also why the "coolers" at the boiling rock prison are effective, they keep all the heat away, preventing firebending. Zuko was able to firebend despite that because of Iroh's "Breath of Fire" technique, which allowed him to use the heat from his own breath.

EDIT: This is why all the talk about breath control is important, firebenders draw in heat with their breath, and then expel it through their limbs as fire.