We often think of memory as a tool for recalling facts, like dates or to-do lists. But the ability to mentally revisit the past is actually one of our most remarkable capabilities, and it evolves throughout life. *Horizon* explores the extraordinary world of human memory, featuring stories from a woman undergoing memory erasure to a man with complete amnesia. The film reveals how these compelling narratives are reshaping our understanding of this fundamental human trait. Ultimately, the discoveries suggest that each of us is defined by our memories.