Renowned author Marlon James is well-known for his vivid and frequently unusual storytelling. His 2015 Man Booker Prize-winning book, "A Brief History of Seven Killings," explores the lives of numerous Jamaicans at various points in the country's history. In this regard, James's understanding of human nature is reflected in the quote you cited.

James frequently examines in his writing how contradictory and erratic people can be. Humans display behaviors that may appear illogical or surprising to others, but are firmly anchored in their individual experiences and hardships, much like a river that abruptly changes its course due to an invisible force beneath its surface.

The quotation alludes to the revelation of unexpected facts about people that may not be obvious from the outside. It implies that occasionally we reveal facets of people's personalities that they might even be trying to conceal from themselves. Similar to discovering secret rooms within a well-known old house, these discoveries can be profound and unnerving.

James uses this quote to highlight the complexity of human nature and the way that our perceptions of other people change over time as new facts become available. This viewpoint inspires readers to see past people's outward appearances and acknowledge that there are always more profound levels just waiting to be revealed.