I think that the most important event is when Steven found out that Jeffrey had leukemia. I think it is important because without this ever happening in the book, and then Steven wouldn't be nicer or treat him better. Also Renee would have never become Steven’s friend and he would have let Renee in to his house to study when she had a cold. Then the concert would have never even raised money for Jeffrey and Steven would have never met Samantha. So pretty much the entire book would have never existed. Or the whole book would have just been him living life.