Kurtz and Marlow are both physically isolated from anyone who is capable of even trying to understand them. Marlow has the ideas of Kurtz, at least, but Kurtz is alone in his thoughts. They are both surrounded by listeners, people who see them as voices, not as human beings. They are not offered anyone's thoughts in return. It is this isolation, this lack of conversation, that drives Kurtz insane. The knowledge of Kurtz keeps Marlow from going insane.

        Kurtz goes unchallenged. In his world, no rational, intelligent, independent person exists. He might as well be the only person, for he is the only entity. The Europeans, the company men, the natives, and the Intended are all people based solely on what Kurtz and others have told them. They have no names, no defining mark in the universe, no soul. They are all the same and can only fight Kurtz collectively and from afar. Kurtz can find no equal among them; he has no one's thoughts to respect and consider. No one seems to be of irreplaceable value, so there is no need for physical consideration of others, no need for restraint. Kurtz's observations of the world and his own self-obsession give him this leave to be wild.

        Marlow is more aware of the world around him than Kurtz. His beliefs are continually tested by the incompetent, the unjust, the foolish, and the liars. At times, he must turn "mentally to Kurtz for relief" from the squaller of civilization. Marlow's restrain comes from knowing that someone out there, Kurtz, is intelligent, thinking, and utterly convinced of something. Marlow is not consciously introspective. He thinks, but he is not absorbed in only himself. Marlow is aware of individual value because he has seen and felt it.

        If Kurtz had Marlow's powers of observation, had been less isolated, he would have been beaten down and bitter, but painfully sane. He would never have "kicked himself free of the earth," "kicked the earth to pieces." Kurtz saw himself as alone, above the rest, and so, he was. Marlow just looked up at him. He knew that he wasn't alone.