Despite the fact that Marlow knows Jim personally and has pieced together the facts of Jim’s life story from Jim himself, Stein, and Gentleman Brown, he remains an unreliable narrator. This is because, as Conrad makes clear, each of Marlow's sources is biased in their own way: Jim romanticizes the events of his own life for dramatic effect (as a young man in search of adventure and fame), Stein is losing his cognitive faculties and also tends to speak in oblique and vague ways, and Brown is a dying, violent pirate who only wants to present himself in the best light. When filtered through Marlow’s own myopic lens, the stories he hears and regurgitates for dramatic effect don’t seem all that trustworthy. When Marlow directly quotes people he has never met (such as the crew members of the Patna who worked with Jim), for example, readers are meant to be somewhat skeptical.
In telling the story through the words of an unreliable narrator, Conrad is encouraging readers to question the very nature of truth. No matter how tirelessly Marlow works to figure out why Jim made the decisions he did or who he was as a person, he will never really know the full story. This comes across in the final pages of the story, when Marlow describes Jim’s death in a letter to the privileged reader:
“They say that the white man sent right and left at all those faces a proud and unflinching glance. Then with his hand over his lips he fell forward dead.
And that’s the end. He passes away under a cloud, inscrutable at heart, forgotten, unforgiven, and excessively romantic.”
The phrase “they say” at the beginning of this passage makes it clear that Marlow does not know what he’s describing to be true but is instead creating it out of stories he has compiled from various sources. In describing Jim as “inscrutable at heart” he also demonstrates an awareness of the fact that, even after studying Jim’s life for years, it is still impossible for him to truly know or understand the man.
