It's fascinating that in just six degrees of separation, you would know approximately everyone in the world. It works on the principle that you know someone, that someone knows someone who you don't know, that third someone knows someone you don't know, and on and on. However, while chains may stretch on forever, you can find some connection with almost anyone to the sixth the degree.
There is this guy, Kevin Bacon, and he even has a game and a charity organization called SixDegrees or whatever. Supposedly, Bacon has been in so many movies with so many different actors that he knows everyone in the movie making industry by like... three or four degrees. I think that's fascinating.
My tend to use two specific trends when I talk about this with people who simply don't understand. A year or so ago, I was really into the "Star Wars extended universe" books and my favorite books where those written by Timothy Zahn, who created both Mara Jade and Grand Admiral Thrawn, the former who is one of the most epic dark-heroines ever and the latter the very best villain ever.
Anyway, I was talking about the extended universe with a friend of mine and she mentioned how her friend's dad was a roommate with Timothy Zahn in college, and they were still friends. Later, I met the friend she was talking about. So, I know Timothy Zahn to the second degree; as I know someone who knows him. So, by extension, I know George Lucas and all those other people by the third and forth degree. Special me. The other example was I know Buzz Aldrin (I think, it's one of those Apollo 11 guys) to the second degree because I met my grandmother's husband at least once, as a baby, and he knew astronaut.
This theory also sort of plays into how small the world is and how you'll know someone and you'll know someone else and then be surprised that those two people know each other. Or something like that. Or you could end up in an airport in Florida and sit down right next to two people from your church and not even know that it's them until they great you (true story) or have a homeschooling family move to Kansas City and completely lose contact until traveling to Kansas City for a supposedly completely unrelated event to discover that said family is involved with the same program that the leader of the event teachers at (true story).
I have a cat climbing all over me. It's very annoying.