In "American Wife" by Curtis Sittenfeld, the narrative explores the complexities of relationships and the often hidden struggles within marriages. The story invites readers to reflect on the seemingly perfect lives of others while acknowledging that appearances can be deceiving. Through the protagonist's journey, the book emphasizes the idea that each couple has their unique challenges and dynamics that outsiders may never fully understand.

The quote, "You never know the nature of another couple's marriage," encapsulates this theme, suggesting that there is always more beneath the surface of a relationship. As the characters navigate their personal lives, it becomes clear that love and companionship can take on many forms, often shrouded in privacy. This insight serves as a reminder of the empathy needed when judging others and the importance of recognizing the unseen struggles that may exist in any marriage.