In "Heart of Darkness," Joseph Conrad explores the profound transition from the known to the unknown. The quote highlights that true wisdom, truth, and sincerity exist in fleeting moments that mark significant shifts in perception or understanding. This transition often occurs when moving from one state of existence into another, particularly from civilization into the wilderness, reflecting the character's journey into the depths of the Congo.

Conrad suggests that these ephemeral moments hold immense value, representing a threshold that transcends ordinary experiences. It implies that through confronting the unknown, individuals gain insights that are essential for personal growth and understanding the complexity of human nature. The novel ultimately illustrates how confronting darkness, both external and internal, can lead to profound truths.