In Cormac McCarthy's "Cities of the Plain," the quote emphasizes the importance of memory and past experiences for individuals who lack certain perceptions. It suggests that those who cannot observe their surroundings must depend on their recollections to navigate situations, highlighting the significance of awareness of one's actions. This reliance on history illustrates a deeper understanding of life and personal choices.

The metaphor of drinking from an empty glass underscores the folly that comes from ignorance or forgetfulness. It reflects the necessity of reflecting on past behaviors to avoid repeating mistakes. This message resonates with the idea that self-awareness and mindfulness are critical for making informed decisions and leading a fulfilling life.