We were told this by every movie, TV show, novel, comic book, video game and song we encountered. When the Karate Kid wins the tournament, his prize is a trophy and Elisabeth Shue. Neo saves the world and is awarded Trinity. Marty McFly gets his dream girl, John McClane gets his ex-wife back, Keanu "Speed" Reeves gets Sandra Bullock, Shia LaBeouf gets Megan Fox in Transformers, Iron Man gets Pepper Potts, the hero in Avatar gets the hottest Na'vi, Shrek gets Fiona, Bill Murray gets Sigourney Weaver in Ghostbusters, Frodo gets Sam, WALL-E gets EVE ... and so on.
Hell, at the end of An Officer and a Gentleman, Richard Gere walks into the lady's workplace and just carries her out like he's picking up a suit at the dry cleaner.
And then we have Star Wars, where Luke starts out getting Princess Leia (in The Empire Strikes Back), but then as Han Solo became a fan favorite, George Lucas realized he had to award her to him instead (forcing him to write the "She's secretly Luke's sister" thing into Return of the Jedi, even though it meant adding the weird incest vibe to Empire). With Harry Potter, J.K. Rowling played with the convention by having the beautiful girl get awarded to the sidekick character Ron, but she made it a central conflict in the story that Ron is constantly worried that, since Harry is the main character, Hermione will be awarded to him instead.