For every beloved movie starring an actor in an iconic, career-defining role, there's almost always a story about how it could have gone very differently. For instance, "Titanic," one of the most successful movies of all time, nearly starred Matthew McConaughey and Gwyneth Paltrow instead of Leonardo DiCaprio and Kate Winslet. Actors constantly turn down roles for one reason or another, and while sometimes that's just business as usual, there are other times when the stars experience major regret.