In the movie, Lara Jean's little sister, Kitty, sends out the letters because she wants to help her sister find some romance. She figures that sending out all five will give her five chances for love. While her reasoning is deeply flawed, her intentions are sweet and very different from Kitty's reasoning in the book. The novel's youngest Covey sister also harbored a crush on Josh, and as revenge on Lara Jean for almost spilling the beans, she mailed the letters.