Curiosity is Marlow’s defining characteristic. It is his desire to explore and fill in the empty spaces on maps that first brings him into the interior. Then, his interest is piqued by multiple mentions and rumors about Kurtz. It urges Marlow to transgress some of his moral boundaries to satisfy his curiosity. His discoveries and contemplation about Kurtz force him to explore his own sense of right and wrong, and expand his tolerance for evil. He brings readers along for the ride when he begins questioning the nature of good and evil by doubting his crew’s decency and entertaining ideas of Kurtz’s integrity.
Marlow’s journey up the Congo River parallels his exploration of the human psyche; as he plunges deeper into the African interior, he similarly plunges deeper into the human psyche and the nature of good and evil.
Marlow’s insatiable curiosity is one representation of his lack of restraint, the flaw he hates so much; thus, Marlow is a hypocrite in accusing Kurtz of such a fault.