I feel this question has to be answered by some reference to John's family situation, and in particular the way that his father is constantly pressurising him to join his profession and ignores John's own desires and ideas for what he what might want to do. Consider how his family situation is presented in Chapter Seven, and how his father brings up the topic of his working with him by suggesting that John goes and works with him after school. John's response indicates the profound lack of communication that occurs between himself and "Bore," as he touchingly refers to his father:
I almost choked on a mouthful of yams when he said that. I mean, I've bene over to the Exchange and seen all the screaming andbarking Bore has to do just to earn a few bucks, and if he thought I was going to have any part of that madhouse, he had another thought coming.
John's problem therefore in part stems from the pressure he is put under to follow in his father's footsteps but also at the same time his desire to follow his own path and explore the things that he is interested in. This leads him to be rebellious and to go against his parents as he seeks to assert his own will and discover his own likes and dislikes.