Sherlock Holmes and Dr. Watson are going camping. They pitch their tent under the stars and go to sleep. Sometime in the middle of the night Holmes wakes Watson up.
"Watson," he says, "Look up at the stars, and tell me what you deduce."
Watson replies, "I see millions of stars, and if there are millions of stars, and if even a few of those have planets, it's quite likely there are some planets like Earth, and if there are a few planets like Earth out there, there might also be life."
Holmes says: "Watson, you idiot, somebody stole our tent!"