I think that Junior's experiences on "the Rez" help him to succeed because they represent an end to which he never wishes to return. Junior recognizes early on that life on the Reservation is not something for someone who has dreams. The confrontation with the teacher proves this. Junior rebels against the fact that the textbooks have not changed, as Junior receives the same text that his mother received. This realization helps him to understand the effect of life on the reservation:
...with the force of a nuclear bomb... [Junior's] hopes and dreams (float) up in a mushroom cloud.
It is not an accidental inclusion of a nuclear device to describe the state of dreams on the reservation. In this setting, being in the world is almost synonymous with a lack of dreams being realized and being nurtured. Junior recognizes this early on. It motivates him to conceive of life at Reardon, in a setting where his own dreams can be realized. At the very least, Junior's experiences on the Reservation encourage him to transform his own reality, in much the same way that he envisions how his cartoons can materialize. Just as he is able to be the author of his own artistic creations, Junior is able understand that his ability to be the author of his own narrative is going to be compromised if he stays on the Reservation. His own limited experiences, combined with his perception of his family and community members as people whose dreams have perished at the hands of the oppressive conditions in life on the Reservation end up fueling Junior in his passion to leave. Accordingly, Junior is able to recognize the zeal and passion in being able to have dreams and to puruse and live them.