Mateo undergoes a transformation over the course of the novel. In the beginning, he is someone who hides from life, choosing to spend his days playing video games tucked away in the safety of his bedroom. Ironically, Mateo doesn’t live until he knows that he will die, and on his End Day, with the help of Rufus, Mateo finds the courage to live in a way that makes him proud. The novel speaks to the idea that the greatest tragedy is not to die, but to die with regrets over a life that was not lived to the fullest. 

Mateo’s impulse to stay safe has prevented him from experiencing life to the fullest. In Chapter 17, Mateo notes that the bird who died “dared to leave his home at least” (95). Unlike that bird, Mateo initially feels as though he has never broken out of his shell—he is trapped in a narrow existence, where he is safe but limited to the confines of his father’s apartment. Mateo is not honest with others or himself, especially about his sexuality. In Chapter 24, Rufus encourages Mateo to let go of his tendency to overthink and to embrace living in the moment: “He’s right.