Chamber of Secrets is Book 2 of the Harry Potter series, so we've already been introduced to Harry. We know that he's embarrassed by all the attention he gets in the wizarding world (he is, after all, famous) and that he defends his friends with everything he's got. In Chamber of Secrets, J.K. Rowling has to give us something new about her central character to keep us interested in his development. It's in this book that Harry starts learning the dark side of his own fame. His first year at Hogwarts has given him some confidence in himself and his friends, but Chamber of Secrets takes some of that easy assurance away from him.
First of all, Harry spends a brutal summer with the Dursleys without hearing any word from his Hogwarts friends. He soon discovers that Dobby the house-elf has been keeping his letters from him in an effort to convince him not to go back to Hogwarts. Yet Harry still spends the summer worrying that "maybe he didn't have any friends at Hogwarts" (1.86). Hogwarts begins to seem like a dream to Harry, proving that his first burst of pleasure in the wizarding world hasn't healed his insecurity about his place in it.
Things get worse as the rest of the school begins to suspect that Harry is the Heir of Slytherin. Harry is an orphan, so he doesn't have parents whom he can ask about his ancestry. What if he is the Heir of Slytherin? Why has he suddenly discovered that he can speak Parseltongue (snake language), Salazar Slytherin's own gift? What's more, the Sorting Hat did suggest that Harry would do well in Slytherin House in Book 1. Does that make Harry evil? Has he been sorted into Gryffindor unfairly? Perhaps he's more like Voldemort than he had supposed….
In addition to Harry's own doubts, he also struggles against the suspicions of everyone else in the school. In Book 1, he discovered that he was famous for something he doesn't even remember doing. Everywhere he goes, wizards and witches recognize him. Harry is embarrassed by all the unexpected attention in Book 1, but, by Book 2, that surveillance takes on a darker edge. In the public mind, Harry Potter is associated with Voldemort. It doesn't take a huge leap of the imagination to think that Harry is like Voldemort; after all, who knows what happened that night when Voldemort tried to kill Harry as a baby? Maybe Harry was too evil for Voldemort himself to overcome. Ernie Macmillan, a Hufflepuff second year, goes so far as to suggest that Harry is trying to become the next Dark Lord.
As Harry deals with his own doubts and the mistrust of the wizarding world, he has to find a new foundation for his faith in himself. In Book 1, Harry is so dazzled by the wizarding world that he has no time to think too much about his place in it. In Book 2, Harry is starting to learn a little bit more about what it will mean to be a famous boy magician. He has to reflect on the choices he has made. Yeah, he chose to be in Gryffindor, but what does that really mean? Yes, he thinks that Professor Dumbledore is the greatest sorcerer who ever lived, but how far is he willing to push that faith?
By the end of the novel, Harry's loyalty to Professor Dumbledore in the face of Tom Riddle's taunts brings Fawkes to him to save his life from basilisk poison. So Harry's huge capacity for faith and love gets an immediate reward. Professor Dumbledore also reassures him: "It is our choices, Harry, that show what we truly are, far more than our abilities" (18.61). Harry's decision to be in Gryffindor separates him from Tom Riddle/Voldemort, no matter how similar their backgrounds and talents may be. While Chamber of Secrets shakes some of Harry's faith in himself – in his own character and in how the world sees him – he manages to rebuild this faith by triumphing over Tom Riddle and winning over the whole school with his success. Of course, this happy ending is only a temporary one: wait until poor Harry gets to the emotional crises of Book 5!