The film switches the infertility from male to female but never explains its cause: environmental destruction and divine punishment are considered. This unanswered question (and others in the film) have been attributed to Cuarón's dislike for expository film: "There's a kind of cinema I detest, which is a cinema that is about exposition and explanations . . . It's become now what I call a medium for lazy readers . . . Cinema is a hostage of narrative. And I'm very good at narrative as a hostage of cinema. " Cuarón's disdain for back-story and exposition led him to use the concept of female infertility as a "metaphor for the fading sense of hope". The "almost mythical" Human Project is turned into a "metaphor for the possibility of the evolution of the human spirit, the evolution of human understanding. " Without dictating how the audience should feel by the end of the film, Cuarón encourages viewers to come to their own conclusions about the sense of hope depicted in the final scenes: "We wanted the end to be a glimpse of a possibility of hope, for the audience to invest their own sense of hope into that ending. So if you're a hopeful person you'll see a lot of hope, and if you're a bleak person you'll see a complete hopelessness at the end. "