At its core, "You Know I'm No Good" is a song about the complexities of relationships, specifically the bind of a love that's both hurtful and irresistible. The track opens with a catchy, repetitive piano riff and builds into a soulful, bluesy narrative that captures the push-and-pull dynamics of a troubled romance. Winehouse's vocal delivery is raw and emotional, imbuing the lyrics with a sense of regret and resignation.