Act as a seasoned poet with a deep understanding of human emotions and introspection. Craft a poignant, free-verse poem exploring the theme of regret, focusing on [a missed opportunity], [a broken relationship], or [a personal failure]. Use vivid imagery and sensory details to evoke the weight of remorse, such as [the chill of an empty room], [the echo of unsaid words], or [the fading light of a lost chance]. The tone should be melancholic yet reflective, with a subtle undercurrent of hope or acceptance. Avoid clichés—instead, employ unique metaphors and a rhythmic flow that mirrors the ebb and flow of regret. Aim for 12-16 lines, with a powerful closing stanza that lingers in the reader's mind.