Living the life you want
One of the major themes of the film is living outside the confines of the routines that we set for ourselves in life. Harold Crick lives every day exactly the same, down to the number of brush strokes he applies to each and every tooth. Once he hears a voice narrating his life to him that says his death is imminent, he decides to change his life completely, and to live the life he always wanted to live. He stops wearing ties to work, he stops counting brushstrokes, he purchases a guitar. At the core of the existential story that organizes the narrative is the theme of living life to the fullest, experiencing all that life has to offer, and enjoying it.
Fiction
Karen's novel about Harold represents a story that she has brought to life, a book that she has had writer's block trying to complete for several years. Funnily enough, her subject and main character exist in real life. They are not fictional entities at all, but real, living people. In this way, the boundary between fiction and reality is breached, and they are interdependent in completely surreal and unfathomable ways. In order to figure out the mystery of his predicament, Harold sets to work learning more about fiction, with the help of a renowned literature professor. In this way, he must fit his life into a fictive narrative. In the end, Karen must choose what to do with her outlandish authorial power. In the film, fiction and its consequences is a major theme.
Making the world a better place
In the beginning, Harold doesn't seem like an especially heroic person. If anything, he is just getting by, going through the motions, and surviving in a job that will pay him enough to allow him to live. By the end, he has become a hero, having thrown himself in front of a bus in order to save the life of a little boy on a bicycle. While Harold may have seemed unassuming and bland, he is actually a heroic person. Thus, the film is interested in looking at the ways that little everyday actions can become heroic, and can make the world a better place. Additionally, Ana Pascal believes in the power of small acts to make the world a better place. A consummate idealist, Ana dropped out of Harvard law when she realized she wouldn't make the world a better place with her mediocre grades. Instead, she chose to start baking cookies, making the world a better place one baked good at a time. Throughout the film, Harold marvels at the ways she is able to gather, help, and feed people with her special baking skills.
The accessories of our lives
In the final lines of her novel, Karen Eiffel writes about the small, seemingly mundane ingredients of our lives that add up to make a life worth living. She mentions the Bavarian sugar cookie that Ana feeds to Harold in his hospital bed, and a slew of other things, before describing the wristwatch that ultimately saved Harold's life. She writes, "And we must remember that all these things, the nuances, the anomalies, the subtleties, which we assume only accessorize our days, are effective for a much larger and nobler cause. They are here to save our lives. I know the idea seems strange, but I also know that it just so happens to be true. And, so it was, a wristwatch saved Harold Crick." In this way, the small mundanities, and how they add up, is a central theme of the film.
Depression
While he might not recognize it, Harold is a depressive character at the start of the film. He lives life so precisely that he is unable to enjoy anything. His depression is revealed in the ways that Karen Eiffel describes his tasks at the office. For instance, the sound of a folder at the IRS calls to Harold's mind "a deep and endless ocean." This is an undeniably depressing image, and betrays Harold's sense of hopelessness and aimlessness. Additionally, Karen Eiffel is reclusive, antisocial, and depressive. An expert on tragedy, she chain-smokes cigarettes and spends most of her days alone contemplating the nature of death. Neither of these characters have especially sunny outlooks, but when their lives intersect, they begin to find the brightness hidden behind the shade of depression.
Control vs. Fate
Harold's interest in precision has a lot to do with his desire for control. In wanting to be able to count every element of his life out and calculate every step, he is able to simulate some degree of control. Once the narrator enters his life, however, he begins to realize how little control he actually has. He sees that free will is something of an illusion, that every action he takes is being authored and is out of his influence. As Harold begins to recognize that he is "a character in [his] own life," he sees the futility of his controlling calculations, and begins to cast fate to the wind. He believes that destiny is out of his hands, that what will be will be, and he cannot try and control his life so much. Thus, an important theme of the film is letting go and accepting fate.
Love
As Jules tells Harold, he has two choices for the genre of his life: comedy or tragedy. Tragedies end with the hero dying, and comedies end with the hero getting married. Having already fallen for Ana Pascal, and looking for a way out of what he believes to be his "imminent death," Harold chooses to make his life a comedy by igniting a romance with Ana Pascal. While the two of them aren't naturally compatible, as Harold begins to open himself up to new experiences and Ana begins to trust him more, the taxman and the anarchist baker fall deeply in love. Romance is a major thematic element of the film, and it is one of the main things that Harold has to live for.
