Isolation
Jack's insomnia and lack of satisfaction in his life stem largely from his isolation. Never does he mention any friends in his voice-over, nor do we meet any. Jack has to attend support group meetings just to experience a human connection. He longs for a place where his feelings can be expressed openly, even if they are dark or sad in nature. He seeks a truth that he is not finding in his job or his day-to-day life.
Like Jack, Marla Singer suffers the same isolation. She doesn't appear to have anybody in her life who is concerned for her. She demonstrates that this isolation doesn't pertain simply to men in society, but to all. Unlike Jack, Marla embraces this reality for what it is. She is poor, living in poverty. She can't turn to a life of consumption to escape her reality because she cannot afford it. Her openness makes Jack uncomfortable. It's like looking into a mirror.
Emasculation
Fight Club presents the argument that men in today's society have been reduced to a generation that does nothing itself, but has become anesthetized with watching others do something instead. Masculinity becomes a brand, a means to sell products to men. "Being a man" then becomes owning the right watch or car instead of knowing who you are and what your values really are.
As a result Jack, Tyler, and the other members of Fight Club reject this spoon-fed approach to living and try to find themselves. By putting themselves through the experience of fighting and facing fear and pain, they hope to strip away the unnecessary and discover their true selves.
Consumer Culture
The film repeatedly critiques the values espoused by advertising: youth, beauty, power, and wealth. Tyler's philosophy contends that people work jobs that they don't enjoy to keep up the appearance of a life that "has it all." In reality these people are deeply unhappy, not simply because this lifestyle does not sustain them in a spiritual sense, but because they don't feel like they can talk to anyone about these problems. Instead, they continue to buy cleverly marketed goods to make themselves feel better.
Coming of Age/Identity
Although this theme traditionally reflects a character's passage through an ordeal in their late teens or early twenties, in the film Jack/the Narrator's ordeal takes place at the age of thirty, making it something of a pre-midlife crisis.
Jack has to come to terms with who he is and must take responsibility for his own lot in life. He instead subconsciously creates Tyler Durden, a charismatic but unhinged id that is free to do whatever he wants. Tyler allows Jack to reject society's expectations but also allows him to reject all responsibility as well. Instead of coming to terms with his place and learning about himself, Jack retreats into a false character, someone he'd rather be. When Tyler goes too far, Jack snaps back to reality and sees that he is losing himself to Tyler. He then must choose to both save Marla and himself from Tyler.
Violence
The fighting in the film is not presented as a solution to the character's problems, but is a means to reaching a spiritual reawakening. The fighting itself reminds the men that they are alive. As part of Tyler's philosophy, it also reminds them that they will die. As part of that philosophy, the men are seeking something of true value, instead of the value system handed down to them by advertising and society as a whole. Fighting is used as a path to reach the core of who they are. As Tyler says to Jack/the Narrator before their first fight, "How can you say you know yourself if you've never been in a fight?" While the fighting can be seen as an attempt by the men to reassert their masculinity, it is more of a rejection of what they have been told masculinity is by prior generations, their jobs, and mass media.
Lack of a Father Figure
In a key scene in the film, Tyler and Jack/the Narrator both bond over their recollections about their fathers. Both men state that their fathers were not a major part of their lives. Jack says that his father left when he was young. Tyler describes his father as a distant figure with whom he would speak on the phone roughly once a year, adding that they are members of a generation of men raised by women. With no distinct male role-models in their lives Jack and Tyler have largely accepted the role of men in society as it has been presented to them by advertising. The aim is to secure a good job with a good salary, get married, and have children. The men of fight club have seen an emptiness in this model and reject it.
Zen Buddhism
Some have seen Zen concepts in the film, particularly regarding breaking the cycle of suffering and the rejection of material possessions. In Buddhist teachings, the attachment to material possessions is what keeps a person attached to this world and prevents liberation. Without this, inner peace cannot be attained. In Buddhism there are generally three characteristics of existence : change, suffering, and a belief that there is no permanent self.
Jack is miserable in his life but is either unsure of how to change or afraid to try. Instead he buries sadness in what he calls the "Ikea nesting instinct," the need to continuously buy products as a means to demonstrate his "strength." Tyler shows Jack that suffering is simply a part of life, but is largely based on attachment to material objects. Jack demonstrates the absence of a permanent self when it is revealed that he and Tyler are actually the same person. Tyler is the persona that Jack wishes to have.
