"No one can ever truly understand the inner workings of someone else's marriage," highlights the secretive and complex nature of intimate relationships. Marriages often contain private struggles, emotions, and experiences that outsiders can never fully grasp, emphasizing the idea that everyone’s personal life is uniquely intricate and hidden from external view.

This quote from J. Courtney Sullivan's book, The Engagements, underscores the mystery that surrounds couples' marriages. It reminds us of the importance of respecting others' privacy and recognizing that what appears on the surface may not reflect the full reality of a couple’s relationship.