Okay, this might be easy. Then again, maybe not.
In the TV series Buck Rogers in the 25th Century, the two-part episode Planet of the Slave Girls featured a character named Brigadier Gordon. At the climax of the episode, both he and Buck share a conversation where Gordon tells Buck that he's been at this sort of thing for a long, long time, way before Buck was born. Buck asks "You think so?" to which Gordon replies: "I know so."
What is the paradox to this conversation?