Gene has a competitive personality, a darker side of himself, that he doesn't like to acknowledge. As a result, he projects his deeply competitive nature onto Phineas. It isn't that he is competitive with Finny and wants to beat Finny and win, it's that Phineas wants to beat him and be number one—or so Gene wants to believe. As Gene suddenly begins to think:

If I was head of the class on Graduation Day and made a speech and won the Ne Plus Ultra Scholastic Achievement Citation, then we would both have come out on top, we would be even, that was all. We would be even.

Gene decides that Finny hates the idea of the two of them being even—Gene as top scholar and Finny as top athlete—and decides that Finny wants to pull out ahead. Suddenly, it becomes clear to Gene that Finny has been trying to sabotage his summer school studies by sucking up all his time with blitzball, the Super Suicide Society meetings, and trips to the beach. His friendship is fake—just a way to bring him down. However, as it turns out, it is actually Gene who wants to bring Finny down.

When Gene realizes that Finny thinks that Gene's brains come naturally to him and that he doesn't have to study to do well in his classes, Gene then decides:

He had never been jealous of me for a second. Now I knew that there never was and never could have been any rivalry between us.

But this too is unsatisfactory to Gene because it means that Finny is a better person than he is, a person of higher character. Gene's jealousy of Finny flares once again. For Gene, the nature of his relationship with Finny is defined by his own sense of competition with this friend. He feels an overwhelming need to win against him, regardless of the cost.

It is just a short time after Gene has decided Finny is not trying to compete with him that he, still jealous and competitive, tries to destroy Finny: he "jounce[s] the limb" that causes Finny to fall. Gene seems disconnected from this action, still more concerned with winning than with his friend's well being right after the act:

Finny, his balance gone, swung his head around to look at me for an instant with extreme interest, and then he tumbled sideways, broke through the little branches below and hit the bank with a sickening, unnatural thud. It was the first clumsy physical action I had ever seen him make. With unthinking sureness I moved out on the limb and jumped into the river, every trace of my fear of this forgotten.

Gene has just done a horrible thing to his friend, but all he can think about is his "sureness" as he jumps in the river, with his fear "forgotten." He can, of course, now forget his fear—his fear of losing—because he has badly injured Finny.

We all have a darker side. Gene dissociates from his own, first through his projection of his shadow onto Finny and then, in a dissociated way (he says "my knees bent," as if this were something he had no control over), jouncing the branch on purpose to make Finny fall. Gene would like to see himself as a good and noble person, but his actions show his darker impulses.

Early in their relationship, Gene becomes envious of Finny's effortless athletic ability and popularity. Gene watches in awe as Finny fearlessly jumps from the high branch of the tree overlooking the river, breaks the school swimming record with ease, and smoothly avoids his competitors at blitzball. Gene cannot contend with Finny's extraordinary athletic ability and begins viewing his friend as his competitor. In chapter 3, Finny persuades Gene to blow off studying for his test in order to visit the beach and relax. At the end of the chapter, Gene displays his competitive nature when Finny calls Gene his "best pal," and he does not respond to Finny's show of affection.

In chapter 4, Gene begins elaborating on his feelings of jealousy, which stem from Finny's extraordinary abilities and his own inferiority complex. Gene misinterprets their friendship and believes that Finny is attempting to sabotage his chances of becoming the best student in their class. Gene's competitive nature alters his perception of Finny and influences him to believe that Finny is more of his rival than his friend. Unfortunately, Gene's sense of competition leads to his decision to shake Finny from the branch above the river, which results in Finny breaking his leg. It is only after Finny's debilitating injury that Gene realizes that Finny was never his rival and was simply a genuine friend. Gene's competitive nature, inferiority complex, and jealousy motivate him to harm his athletic, extrovert friend, which indirectly causes Finny's death.

During the events leading up to Finny's accident in A Separate Peace, Gene's acute sense of competitiveness strains his relationship with his friend Finny.

Gene feels that he consistently fails to measure up to Finny's athletic ability and charm.  Even though Gene is very academically gifted, he wants what Finny has--and pushes himself to achieve it. His growing resentment of Finny's talent and subsequent need to compete to prove himself is evident in Chapter four as the boys go back and forth on why Gene studies so hard.   Finny points out that it's because Gene "want[s] to be head of class, valedictorian, so [he] can make a speech on Graduation Day" (43). 

Gene secretly concludes to himself that this "was a pretty good goal to have,"  realizing that if he were the top academic student, then he and Finny would be "even, that was all" (43).  In Gene's mind, he perceives the possibility that Finny "minded, despised the possibility that [he] might be the head of school."

The thought that Finny might be sabotaging his academic efforts hits Gene hard.  Knowles uses a bomb metaphor to relay the destructive power of Gene's negative thinking:

"like a detonation went the idea of any best friend, up went affection and partnership and sticking by someone" (44-45). 

Gene's competitive need to prove himself against Finny breeds resentment and self-doubt of the genuinity of their relationship.