In their final moments together before he dies, it is Finny himself who manages to find a way to accept Gene's betrayal. After breaking down, Finny cries and struggles to find a way to understand what has happened to him. He says to Gene:
It was just some kind of blind impulse you had in the tree there, you didn't know what you were doing. Was that it?
Gene replies instantly, "Yes, yes, that was it. Oh that was it . . . ." Finny continues to convince himself:
I think I can believe that. I've gotten awfully mad sometimes and almost forgotten what I was doing. I think I believe you, I think I can believe that. Then that was it. Something just seized you. It wasn't anything you really felt against me, it wasn't some kind of hate you've felt all along. It wasn't anything personal.
In other words, Finny convinces himself that Gene never meant to hurt him because that is what he must believe.