In Albert Camus' novel "The Stranger," the protagonist's actions and feelings often reflect a deep sense of estrangement and existential angst. The quote about "knocking four quick times on the door of unhappiness" symbolizes the abrupt and jarring nature of confronting one's own emotional state. It suggests a relentless pursuit of understanding or addressing unhappiness, echoing the protagonist's struggle with their own identity and the absurdity of life.

This moment serves as a poignant reminder of the way individuals can confront their inner turmoil. The imagery of knocking illustrates a forceful entry into the realm of discomfort, emphasizing how often people must face their unhappiness head-on. Ultimately, this echoes the central themes in Camus' work, exploring the disconnect between personal feelings and societal expectations.