One thing we know from Sherman Alexie's young adult novel The Absolutely True Diary of a Part-Time Indian is that tribe members are expected to be loyal to the tribe. Though things are difficult in the tribe and though there is no way to escape the poverty of the reservation except by leaving the reservation to pursue one's own dreams, the tribe expects its members to stick things out and remain loyal. Hence, the tribe expects all tribe members to behave in such a way that loyalty to the tribe is put first.
We especially see this when Junior decides he wants and deserves more of an education than the reservation can provide and leaves to start attending Reardan, the white kids' school. We particularly see the expectancy of loyalty to the tribe expressed in the reaction of his best friend Rowdy when Junior tells Rowdy he is leaving their reservation school for Reardan. Rowdy cries, screams, says he hates Junior, and punches him in the nose. Another time, walking home from attending school at Reardan, Junior is jumped by three guys from his tribe. Junior narrates for us his experience of being treated like a traitor:
I could tell they didn't want to put me in the hospital or anything. Mostly they just wanted to remind me that I was a traitor. (p. 79)
Hence, as we can see, loyalty to the tribe is of utmost importance, and Junior is acting very bravely by breaking away and trying to escape from poverty and lack of education.