In Cormac McCarthy's novel "All the Pretty Horses," the quote "You don't know shit from apple butter" highlights the ignorance or lack of understanding of the speaker's audience. This colorful expression illustrates not only the speaker's frustration but also emphasizes a clearer distinction between knowledge and ignorance in a vivid, memorable way.

The phrase signifies a deeper theme within the book, where characters often grapple with their own experiences and the realities of their surroundings. It reflects the journey of self-discovery and the lessons learned through hardship, showcasing McCarthy's exploration of the human condition and the complexities of life.