system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar: The Last Airbender / Legend of Korra] Are souls simply a kind of spirits reincarnated (usually) forever or are they something different in substance and nature?

The world is made of earth, fire, air and water with spirits being kind of something else but are souls something like spirits or are they specified to really be distinct in nature?

I know that a few people have escaped the cycle of reincarnation and basically became spirits so I'm curious about what that really means.
gpt
Every person has a spirit that contains their consciousness, which can be thought of as a soul. If they are skilled enough, they can travel to the spirit world, leaving their mortal body behind. Upon death, a person's spirit is reincarnated, and they lose their consciousness, unless they have some sort of tether, such as the Avatar. Whether or not it passes on to some other plane/realm is unknown. Some, like Iroh, choose to leave their mortal bodies behind and continue to exist as spirits in the spirit world, and are not reincarnated.