Each of the five main characters in The Heart Is a Lonely Hunter strives to break out of his or her isolated existence. The reasons each character is isolated are very different: the deaf-mute John Singer cannot communicate with most of the world because he cannot speak; Mick Kelly cannot communicate with anyone in her family because they do not share her intelligence and ambition; Biff Brannon is left alone when his wife dies; Dr. Copeland is alienated from his family and from other black people because of his education and viewpoints; Jake Blount is alone is his radical social viewpoints and in the fact that he is a newcomer in town.
The isolation from which each character suffers is a combination of personal and environmental factors. However, all of the characters feel profoundly alone in some sense or another, and all of them desperately need to communicate their feelings with somebody who understands them. All five, with the exception of Biff, confide in Singer the things that make them spiritually lonesome. Though it is never made clear, the only reason Biff does not discuss his personal conflicts with Singer is most likely because Biff himself is unable to articulate these personal conflicts. Regardless, Biff still finds Singer's presence comforting. After talking to Singer, the characters almost always feel soothed.
McCullers also uses the novel to explore the idea that all people feel a need to create some sort of guiding principle or god. However, whatever each person conceives of in this godlike role is merely his or her own fantasy; it has no basis in reality, just as those who believe in God have no proof that He actually exists. Singer becomes a pseudo-religious figure for the main characters of the novel; they believe he has infinite and unending wisdom about many things, and they turn to him in times of trouble, constantly asking him to help them achieve their goals and assuage their fears and doubts.
Each character creates a different god in Singer. For Mick, Singer is a man who feels as she does about music and whom she can ask very personal questions—things she has never said to anyone before. For Dr. Copeland, Singer is an the only enlightened white man he has ever met, the only one who understands the Doctor's burning passion to achieve justice for black people in the world. For Blount, Singer is a man who shares his deep concern about the importance of socialist revolution and the eradication of capitalism. For Biff, Singer is, like Biff himself, a quiet and astute observer of the human condition who ponders many things in great depth.
In reality, however, Singer is none of these things; he is merely an ordinary, intelligent man who only wants to be with his friend Antonapoulos. Singer cannot understand why all these other people come to him for advice on topics with which he has no expertise or even familiarity. It is ironic that Singer—a character the others blindly make out to be a sort of god—is just as prone to the same blind faith, which we see in his love for Antonapoulos. Singer believes that Antonapoulos is a wise, kindhearted person, and he worships his friend unremittingly. Meanwhile, it is clear to us that all the evidence suggests Antonapoulos is actually coarse, selfish, and lazy. In the end, we see that all the major characters are deluding themselves by believing only what they wish about John Singer. Nonetheless, the very fact that they believe it gives them peace.
Heroism surfaces most overtly in the novel in the characters of John Singer and of Mick, the least self-absorbed of the major characters and seemingly the only ones capable of feeling genuine, unselfish love for another person. The love Singer feels for Antonapoulos demonstrates the altruism of Singer's nature: he is capable of loving someone completely without receiving any true reciprocation whatsoever. Mick also shows herself to be capable of loving someone for reasons that are not at all self-interested: she feels a deeply affectionate love for her younger brother Bubber, and she continues to feel this way even when he distances himself from her.