Brinker's reason for this relentless questioning about the tree incident is to tear Gene apart from Phineas. Brinker's meddling upsets the symbiotic balance of Gene and Phineas" relationship. Brinker ultimately achieves the separation that he desired when Phineas dies. Brinker's immaturity exhibits itself in this act of revenge that forever changes Devon. .
Phineas lives a life of freedom and spontaneity at Devon that helps to reveal his true innocence. Like Brinker, he struggles with immaturity and can hide under the sheltered veil of Devon. The most daring idea that Finny has is to jump from the tree. This haphazard, spontaneous idea is the kind of childish thought that comes without any concept of consequence. It was his idea, so "naturally, Finny was going to be the first to try" (7) the jump. The thrill and excitement Phineas gets from this first jump leads to his desire for more jumps. He decides to create a "suicide society," with the requirement for membership being "one jump out of the tree" (24). While up in that tree, Gene's "knees bent" (52), a subconscious action that causes the ultimate damage to Finny's life. Because of the jouncing of the limb, Finny falls hard to the ground and breaks his leg, his "first clumsy action" (52) ever. "Sports are finished for him" (55). Finny is now physically unable to do what he loves best and has lost his signature athletic walk. Finny "used to be aiming for the Olympics" (109) and now has to face his shattered dream. Finny shows a substantial growth in maturity when he makes the best of this situation. He decides to coach Gene for the Olympics instead. Now Phineas must fulfill his passion in sports by "living through" Gene. When Gene and Finny form a team, Gene begins to grow, both physically and mentally.
Phineas is the catalyst in Gene's transformation from a simple conformist to a mature adult. Phineas throws Gene into various conflicts, forcing Gene to resolve them.