How does their assertion affect them and the book as a whole?
I thought Gene stood up for himself and his own right to be who he wanted to be instead of being dragged in the shadow of Finny. So he was driven to make Finny fall from the tree.
What are your opinions?
Brinker certainly maintains his convictions against the war despite pressure from others. Determined to expose Gene for his nefarious deed, Brinker arranges the mock trial.
Leper finally stands up for himself and in doing so seems to vindicate his character. Life is not over for Leper, but just beginning. This is true for all the characters with the obvious exception of Phineas.
All the boys are finding themselves and in doing so finding their own way out of childhood.
Peer pressure is difficult, especially for the teenage years. Sometimes just being different is standing up for oneself. Finny stands up for himself by being different in this case, and pays the consequeces for it.
I think that the characters in the text are very much like "real" people in life. There are times where we (they) can stand up for ourselves (themselves) and other times where we (they) feel too overcome by what is going on to be as strong as we (they) can.
Therefore, I think there are times in the text where both Gene and Finny assert themselves and other places where they cannot.