What is the nature of man in A Separate Peace by John Knowles?

In the final chapter of his novel John Knowles's narrator,
Gene Forrester concludes from his return to Devon
School,

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Because it seemed clear that wars were not made
by generations and their special stupidities, but that wars were made instead by
something ignorant in the human heart.

Only Phineas never
was afraid, only Phineas never hated anyone. Other people experienced this fearful shock
somewhere, this sighting of the enemy, and so began an obsessive labor of defense, began
to parry the menace they saw facing them by developing a particular frame of
mind.

Certainly, much hatred
is born of fear and envy and a sense of inferiority, and it is this truth that Gene
realizes upon his return in order to retrace his life at Devon School. Confronting the
the superiority of athleticism and popularity and joie de vivre in
the person of Phineas, Gene fears the competition that Finny presents him.  He also
feels that Phineas is jealous of his academic success, and fears that Finny takes him
from his studies at night to participate in the Secret Suicide Society in order to keep
him from good grades.  But, when Finny encourages him one night to study rather than
join in the society's activities, Gene realizes that Finny has never envied him. 
Instead of being relieved, however, Gene finds this knowledge intolerable as it points
to his own inferiority of character. Then, Gene becomes envious of Finny,who is "too
unusual for rivalry." And, it is in this state of envy, that Gene jounces the limb,
causing Finny to fall and break his leg; it is because of that "something ignorant in
his heart" that Gene harms his good friend, Phineas, with whom he wages his private
war.