Like most boys his age, Jerry is desperate to fit in. He wants to prove himself in front of the other boys to show them that he is not what they would regard as a sissy. Swimming through the tunnel is an important rite of passage, one that will represent an important checkpoint on Jerry's long, complicated journey to manhood. Although it will present quite a challenge—and a potentially dangerous one at that—Jerry knows that if he is to prove himself to the other boys, there is simply no way that he can turn back.
But as the story progresses, Jerry no longer wants to swim through the tunnel to impress the other boys; he now wants to do it for himself. In completing the challenge, Jerry has not just matured considerably, he has also become an individual. This rite of passage is essential to his identity and self-worth. But more than that, it is been an assertion of Jerry's individuality—something special and unique that does not depend on the approval of others.