Predetermined versus Self-directed Fate
Travis frequently changes his view of whether he is in control of his destiny or whether his destiny is predetermined. In the beginning of the film, Travis complains about being lonely and not having any place to go. He tries to control his own fate and change his situation by getting a job and finding a girl. When Travis's plans don't turn out the way he hoped, he shifts the blame away from himself by professing a belief in predestination, claiming he fails because he is meant to be "God's lonely man." By the second half of the movie, Travis has given up on the idea that he has any control over what he does. When he leaves his apartment with the plan of killing Palantine and himself, he notes that this is his destiny and that he never had any choice. Yet he fails in his goal of shooting the candidate, which suggests that Travis's theory about destiny is flawed. Travis creates a new fate for himself by killing Iris's protectors, a decision he makes on his own. Travis, not God, creates this destiny.
Other characters, such as Iris and Wizard, have their own views about how they might change their destinies. Wizard adheres to a more passive philosophy of life, as he tells Travis he'll always be a taxi driver no matter what he does. Travis does indeed remain a taxi driver, which suggests that he may not have as much power over his fate as we might expect. Iris is powerless in many ways, and while her fate may not be predetermined, it is certainly influenced by other people. Sport manipulates and uses her, refusing her the freedom of choice, and Travis forces freedom on her whether she wants it or not. Though Iris came to New York in an act of independence, by the end of the film she has lost control of her destiny.
Loneliness in Crowds
Among the millions of people in New York City, meaningful personal connections can be few and far between, and in Taxi Driver we see several cases of such urban isolation. Travis resents that the people in his cab pretend he doesn't exist, and in a way, New York itself is an extension of the little world of the taxi: The city is full of people who don't pay attention to each other and who pretend Travis isn't there. Travis isn't the only lonely character in the film. Tom and Betsy flirt with each other, but they don't seem to share a true personal connection. Betsy is lonely enough to consider a date with Travis, a stranger who approaches her from the street. Wizard and the other cabbies congregate at an all-night diner, hinting that they don't have families or stable home lives. The only true relationship in the film is between Sport and Iris, and that relationship is based on illegal exploitation. Taxi Driver contains many shots of crowds, each person going in his or her own direction. To some extent, this view of New York reflects Travis's warped, isolated perspective, but he is not alone in feeling lonely.
The Glorification of Violence
Taxi Driver's surprise ending portrays society's glorification of Travis's violence. Instead of dying in the shootout, Travis survives and becomes a local hero, despite having murdered several people in cold blood. The film shows several press clippings hanging on the wall of Travis's room as well as a thankful letter written by Iris's parents. Ironically, Travis, the perpetual social outsider, becomes celebrated in society by violating its laws. The law-abiding Travis was invisible, but the murderous Travis is a hero. In a way, this plot twist validates Travis's criticisms of New York society, which tolerates and even praises violent criminal behavior. Only by acting violently could Travis escape the loneliness that seemed to be his fate.