Christopher Nolan explores the nature of memory with his twisting and turning Memento timeline. As a director, Nolan has prioritized originality and examines themes that fascinate him as a storyteller. Nolan's interest in time and memory, and how these factors color the perception of the world and everyone in it, can be traced back to his breakout hit Memento. His second feature film after the crime-thriller Following, 2000's Memento stars Guy Pearce as Leonard Shelby, a man with anterograde amnesia (the inability to retain memories of recent events) ever since two men attacked him and murdered his wife.
https://screenrant.com/memento-timeline-ending-leonard-sammy-explained/