It is immediately obvious that Hazel isn't the typical teenage girl from Indianapolis. She is—conscientiously speaking—old for her age, as we see when she's contrasted with her friend Kaitlyn. By comparison, Hazel is far more thoughtful and considerate about her actions than Kaitlyn, and she is far more analytical. One of Hazel’s defining characteristics is her wish to tread lightly upon the world. She desperately wants to mitigate the harm caused by her existence on Earth. Though this outlook on life is dramatically different from Augustus’s, over the course of the novel the teens are able to learn a lot from one another.
Hazel’s transcendent journey throughout the novel is truly multifaceted. Physically speaking, we witness Hazel grow weaker. This change is apparent in the fact that she uses the stairs at Support Group at the beginning of the novel and opts for the elevator near the novels end, as her physical condition deteriorates. The more nuanced aspect of Hazel’s journey revolves around her spiritual and philosophical understanding of death. At the beginning of the novel, Hazel obsesses over the impact her death will have on those around her. She fears getting close to anyone because she knows that her death, which isn't far off, will hurt anyone close to her. It makes her, as she puts it, a “grenade.” This fear appears most in regard to her mother. Once, when Hazel was near dying, she overheard her mother saying if Hazel dies she won't be a mother anymore, and that thought has stayed with Hazel. This fear motivates Hazel's mission to determine what happens to the characters at the end of An Imperial Affliction. She needs to affirm that everything turns out alright for Anna’s mother, so that she can convince herself that her parents will end up alright.
Through her relationship with Augustus, however, Hazel's perspective changes. When his cancer reappears, she recognizes that, of the two of them, he is now the grenade. But even so, she isn't sorry she fell in love with him, even though it will hurt her immensely when he dies. Instead, she cherishes and feels extremely grateful for the time they do have together. The final words of the novel indicate the extent to which Hazel grows spiritually throughout her journey. The implication of the words “I do” are of a marriage that takes place through memory. Though the marriage is symbolic, it is nevertheless real. What Hazel means by saying “I do” is that she will remember and love Augustus for as long as she lives, and in that sense she has learned that death is not the ubiquitous finality she had once considered it to be. Our relationships continue, even if we do not.