My husband had an interesting thought... and he actually
told it to me!
Locke keeps saying they were all brought there for a purpose. Well, Hubby mentioned that all the characters seem to have issues with their fathers. Jack and his alcoholic dead(?) father, Sawyer' father killing his mother then committing suicide, Sun's father in organized crime. Hubby thinks Kate might have killed her father and that's why her mother was so afraid of her. Hurley's father wasn't in the picture, but we know that he had "issues" because he was in the mental ward. John Locke's father used him for a kidney.
Hmmm...