In Susan Cooper's "Silver on the Tree," the quote reflects on the dual nature of darkness and light. It suggests that darkness only affects those who are at the fringes of experience: those who are either overly enamored with their own bright ideas or those consumed by their own negative thoughts. This highlights a struggle between being open to possibilities and being trapped in one's own mind.

This passage can be interpreted as a commentary on human behavior and perception. It implies that individuals who are too focused on their own beliefs may become isolated or blinded to reality, while others may feel overwhelmed by their inner turmoil. Ultimately, the quote invites readers to consider how they engage with their thoughts and the world around them.