d04f9e2c_r__The_Last_Airbender_resource__Aang_s_experience
[Chakra] Light Chakra [Deals with] Insight [Blocked by] Illusion [Location] Forehead [Aang's experience] 
Guru Pathik began by explaining that the greatest illusion of the world was the one of separation; things thought to be separate and different were in fact one and the same. Aang instantly connected this concept with the four nations and Pathik told him that every individual was part of one collective people, yet lived as if divided. Aang realized that Pathik was saying that everyone was connected, thus making divisions meaningless. Pathik continued to explain that even the separation of the four elements was an illusion, as they are four parts of the same whole. He continued by stating that even metal was simply refined and purified earth, concurrent with Toph's discovery of metalbending elsewhere.
Chakras - Avatar Wiki, the Avatar: The Last Airbender resource
Aang's experience