In her book "Because It Is Bitter, and Because It Is My Heart," Joyce Carol Oates explores the complexities of truth and human perception. The quote "For once a truth is known it cannot be unknown; it can only be denied" highlights the enduring nature of truth in our lives. Once we become aware of a reality, we can no longer ignore it, though we may choose to deny its existence. This realization brings a profound impact on our understanding of ourselves and the world around us.

The idea emphasizes the struggle individuals often face when confronted with uncomfortable truths. People may opt for denial as a coping mechanism, yet the truth lingers in their consciousness, shaping their thoughts and actions. Oates skillfully navigates these themes, offering readers an introspective look into the human condition and the inherent challenge of accepting what we know deep down to be true.