Yesterday by The Beatles is a poignant reflection on lost love and the irreversible passage of time. With a melancholic melody, Paul McCartney sings about a past relationship that ended abruptly, leaving him longing for the simplicity and happiness of 'yesterday.' Key themes include nostalgia, regret, and the bittersweet nature of memories. Particularly poignant moments in the song are lines like 'Why she had to go, I don't know, she wouldn't say,' which express the lingering confusion and heartache over the lost love.