The Truth Hurts.
Throughout life most people, at one time or another, have trouble accepting the truth. John Knowles apparently had this in mind when he created Finny's character. He is the epitome of someone in denial; denial of imperfections. Finny's greatest encumbrance is his inability to accept the reality of things.
From the beginning Finny denied that there was a war going on around him. He simply brushed it aside as a joke. He said, "The fat old men who don't want us crowding them out of their jobs. They've made it all up." (107). The war held an abundance of imperfection that Finny could not allow into his spotless picture of life. Everything about the war was too serious, and all too tragic for him to handle.
Gene openly admitted to Finny that he shook the tree and caused Finny to fall out. However, this confession was impossible for Finny to take in. He could not be convinced that Gene would commit an act that traitorous to him since they are best friends. He cannot familiarize with this flaw in Gene. Finny said 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?" (183). This vision of the accident as a "blind impulse" allows Finny to uphold his impeccable view of his best friend, again protecting himself from imperfection.
Futhermore, Finny refused to accept that he was inadequate for anything. He admitted to Gene that he had sent numerous letters to the Army, Navy, and Marines. Everyone rejected him for the war and that is what made him deny it. He said there would not have really been a war to him until he was able to enlist. Finny always knew in the back of his mind that the world was at war, but he knew he was inadequate for it and that was almost impossible for him to conceive.
So, Finny's greatest encumbrance is his inability to accept the reality of things.