d04f9e2c_r__The_Last_Airbender_resource__Aang_s_experience
[Chakra] Fire Chakra [Deals with] Willpower [Blocked by] Shame [Location] Stomach [Aang's experience] 
Guru Pathik proceeded with the unlocking of Aang's third chakra by asking the Avatar of what he was ashamed and for what reason he was disappointed in himself. Aang had a vision of when he first attempted firebending and severely burned Katara's hands. He told Pathik that he would never firebend again. Pathik responded that in order to obtain balance, he must accept all the aspects of his life. Aang was the Avatar and therefore he was a firebender. Aang accepted his duty and successfully opened the third chakra.
Chakras - Avatar Wiki, the Avatar: The Last Airbender resource
Aang's experience