Although this does not necessarily imply that Cockroach is derivative, there is a suspicious similarity between the protagonist's experience and the experience of the protagonist of another important existentialist novel—one of the most important in the genre, in fact: The Metamorphosis, by Kafka. In that book, a salesman is literally transformed into a cockroach, but his experience of reality does not change as much as it might seem at first. In this book, that premise is inverted; the protagonist here is still a human, but his experience of reality has turned into a roach's.
It is important to the unnamed protagonist's character development that his therapist does not really understand him. There are many ways of reading the symbol. First of all, Genvieve is not sympathetic whatsoever to his plight, so perhaps this is an expression of the protagonist's feelings about women; even trained women who are specifically able to understand different kinds of minds are unable to understand his truth and his point of view. After that, the gender falls off. Does anyone understand his point of view? Does anyone understand anyone else's point of view at all?
The inclusion of suicidal despair, romantic agony, rape, abortion, and murder complete the existential portrait of life. After these kinds of sufferings are remembered, the existential dilemma is fully explained. Not only do we suffer loneliness, but the quality of our lonely points of view are often so full of pain and suffering that we must wonder about the true nature of human life and human experience. The protagonist helps clarify that question by committing murder. By murdering Shohreh's rapist, he establishes a personal standard about the worth of human life. He values experience of reality more than actual life, because he rewards rape with murder.
