When They Said It:
Obi-Wan is explaining to Luke his family history and George Lucas is planting seeds among the fanboys for the many prequels to come.
When You Can Use It:
Any time the kid disagrees with you, their mother, their sibling, their teacher — pretty much anyone until they're old enough to get the reference when you say, "That's just like your opinion, man." It's also useful in the event that you have to explain the whole "That girl you have a crush on is actually your twin sister, from whom you were separated at birth" thing.
