The quote "Who is at a good tree, good shadow shelters him" from "Don Quijote of La Mancha" by Miguel de Cervantes Saavedra speaks to the idea of seeking support and protection in life. It suggests that being in a favorable situation or surrounded by good influences can provide a sense of security and comfort, much like how a tree offers shade from the sun. This metaphor emphasizes the importance of choosing the right environment and companions to thrive and find refuge from life's challenges.