How did the opening passage of the book (first paragraph up to first chapter) lead you to anticipate the ending of the book?

The very first passage in On Agate Hill is a letter from drop-out college student Tuscany Miller to her professor explaining why she dropped out and why she is asking to be let back into the program and continue her thesis. She says she found a box with a diary and some letters as well as other "phenomena" belonging to Molly Petree, and she would like to share them with her professor. After reading this letter, I expected that Tuscany and Molly would share some common history, or perhaps be going through the same experiences. This hasn't seemed to prove very true yet, except for the fact that they both have interesting family lives (Tuscany's father left her mother for another man then got a sex change, and Molly was an orphan who's uncle then died and was sent to boarding school by her father's friend and her mysterious benefactor whom she did not see until her graduation 4 years later).

This letter from Tuscany was really funny, and I was expecting the rest of the book to be funny. It's not. Some parts are downright depressing. The first part is written by Molly herself and is about her broken home life. The second part is written by the headmistress of Molly's school, who hates Molly for reasons never clearly expressed. She has a mildly abusive husband and has approximately 10 children by him, at least two of whom died, before being admitted into a mental hospital. The third part is written by Agnes, Molly's friend and a teacher at her school. She writes about her and Molly's search for a teaching job after they leave the old school.