Sherlock Holmes and Doctor Watson are out on a camping trip. They trudge all day, covering lots of miles, and finally decide, just as dusk is falling, that it's time to set up camp for a night.
They put up their tent, start a fire, cook a simple meal, eat, and both being exhausted from the day's exertions, decide to go to sleep.
At about 3 in the morning Holmes shakes Watson awake and says, "Watson, look up at the stars in the sky and tell me what you deduce from them."
Watson is sleepy, but he has learned that there is always a point to even the most random of Holmes's questions, so he does as he's told, and gazes up at the stars.
"Well, Holmes," he says after a moment, "I can see millions of stars. Millions of them. And I guess if there are millions of stars, then around many of those stars there must be planets. And if there are planets around those stars, then some of those planets must be like our planet. And if planets like ours exist around some of those stars, then on some of those planets there may well be people, looking up at the stars and imagining that we exist as well. That's what I deduce from looking up at the stars, Holmes."
And Holmes says, "No, Watson, you fool -- someone has stolen the tent."