The quote reflects a deep sense of irony and involves the complexities of relationships. It suggests that pursuing someone who is already involved with someone else is not just reckless but also misguided. The folly lies in the fact that you are choosing someone who has demonstrated a lack of commitment by leaving another relationship. The emotional implications of such choices can lead to heartbreak and further complications.

In Jodi Picoult's book "Mercy," this theme resonates with the characters' struggles, illustrating how decisions driven by desire can lead to painful outcomes. The narrative delves into human emotions and moral dilemmas, emphasizing that love is often entangled with personal histories that affect current choices. Ultimately, this quote encapsulates a cautionary sentiment about infidelity and the risks of pursuing love under complicated circumstances.