Atonement - Assessment of Briony ‘s Bildungsroman or “Coming of Age”

At first, Briony is characterized as a young girl who has been very sheltered throughout her life and is unaware of the proceedings of the world. She is caught between reality and fantasy and does not know which one is real. As the story progresses, Briony begins to question her purpose in the world and decides to stay on the bridge until something real and meaningful happened to her. 

This happens when Robbie gives her the letter to give to Cecilia. Whens Briony succumbs to curiosity and reads the letter, she sees something that she has never seen before and does not understand and perceives it as something so horrible that she immediately feels the need to protect her sister Cecilia from this monster that she thinks Robbie is. I also think that this letter brings up extreme jealousy in Briony as she finally realizes that Robbie does not love her, but instead loves her sister. So maybe Briony goes after Cecilia and Robbie as a form of protection or maybe to try and stop anything occurring between Robbie and Cecilia due to jealousy, who knows. But this is the point when Briony has her "coming of age" and realizes that the world isn't all about her and that people have their own problems just like her.