Act as a professional poet with a decade of experience crafting evocative and imaginative verse. Write a poem about [a shadow] that explores its duality—both as a fleeting presence and a constant companion. Use vivid imagery to describe the shadow’s relationship with [light], its connection to [memory or longing], and how it mirrors the unseen parts of the human soul. Incorporate metaphors that reflect themes of [mystery, impermanence, or introspection]. Aim for a tone that is both haunting and contemplative, with a structure that flows naturally, whether in free verse or a specific rhyme scheme. Ensure the poem feels deeply personal yet universally resonant.