What is one effect that an in medias res opening is meant to have on the reader?

One effect that an in medias res opening is meant to have on the reader is to immediately grab their attention and create a sense of mystery and intrigue. By starting a story in the middle of the action or conflict, the reader is immediately thrust into the heart of the narrative, leaving them eager to learn more about the characters and their motivations. This technique can effectively hook the reader and keep them engaged as they are drawn into the story to uncover what led up to the opening scene.