In The Absolutely True Diary of a Part-time Indian, what forces drive the dichotomy of Junior's perception of his world and allow him to see the land in apparently disparate ways?

The forces that drive the dichotomy of Junior’s perception are his keen observation and reflection and his consideration of how others perceive the reservation.
Junior is a writer, and writers observe and reflect on the world around them. His world is split between “the rez” and the world that he experiences at Reardan, the white school. When he is on the reservation, there are times that he observes his community and see the beauty of his culture. We see this when he sits on the hill and looks down, reflecting on the beauty of the land. It helps him to understand why it is loved. Another scene that shows this is when the wealthy white man, Ted, tries to return the powwow dance outfit at Junior’s grandmother’s wake. The outfit does not belong to his people or his grandmother, and this sends all attendees into laughter. Arnold observes the warmth and tenderness of his people, despite the sad event. Another major scene that shows how his observation and reflection affect his perception is near the end, when he reflects back on time he and Rowdy spent near Turtle Lake. He is reminded of the wit in the stories told about this place and remembers appreciating the land when he is perched high up in the tree.
Despite the beauty in the land and the culture that Junior can see, when he is in the “white world,” he observes how that community views his land. He can see through the eyes of fellow students how impoverished, dangerous, and dead-end this place can be. He can see the rampant alcoholism, the lack of avenues for success, and the apathy when he views his land from the Reardan perspective. He can put himself in his classmates’ and teachers’ shoes and see how they see his world (like when he misses school because he has no ride, or when he has nothing to eat for lunch, or when he must relay that yet another family member or friend died due to alcohol, whether directly or indirectly). And he does agree with some of the perceptions held by the “white world” which create this disparate view of his homeland.

In The Absolutely True Diary of a Part-time Indian, Junior sees the reservation in "apparently disparate" ways because he understands the cultural beauty and socioeconomic difficulties that are simultaneously present in life on the reservation. For example, in one scene, Junior sits on top of a high hill looking out over the reservation, and he feels a sense of love for the beauty of the landscape. He understands his people have a strong attachment to their land and families, which is why people—even in the face of adversity—choose to remain living on the reservation. Junior also understands there is a significant lack of opportunities for education and employment on the reservation, which creates problems such as the rampant alcoholism that claims the lives of many people Junior knows. Junior's decision to leave the reservation to go to school at Reardan is not motivated by hate or disgust for the reservation—he simply wants to have access to better opportunities. He loves the cultural and familial ties he has to the reservation, and this love motivates the disparate views he has of his life on the reservation.