The Secret Life of Walter Mitty (1947)

Walter Mitty, a daydreaming pulp-fiction writer with an overprotective mother, likes to imagine that he is a hero who experiences fantastic adventures. His dream becomes true when he accidentally meets a mysterious woman who hands him a little black book. According to her, it contains the locations of the Dutch crown jewels hidden since World War II. Soon, Mitty finds himself in the middle of a confusing conspiracy and has to admit that being a hero in real life isn't that easy.