How does the shifting point of view in Heart of Darkness help the reader discover the narrator's psychological being?
I think that it is deliberate on Conrad's part to not give us a point of view where psychological totality is present. In my mind, one of Conrad's fundamental points in his novel is the danger that lurks with a totalizing vision of absolutism, and the terror it can impose. Kurtz and European "enlightenment" were seen in this totalizing light and the result was disastrous for both the indigenous people of the Congo and for Kurtz, himself. Conrad avoids this same trap with presenting a point of view framework that consists of many voices, and not one becoming a source of totality. There is Marlow, whose voice is most dominant. There is also the narrator who opens the story, and who allows Marlow's voice to become evident. There is also Conrad, himself, who brings all of these voices to the forefront. In the end, there is no singular narrator, no force of totality. Rather, there are multiple voices and there is a level of incompleteness in all of them, leaving it up to the reader to assess in their own mind which is most reliable. In constructing his narrative in this manner, Conrad has been able to accomplish a significant achievement in both style and theme.