Why have humans never found aliens?
economist.com

The Economist reports on a recently published astronomy paper:

Dr Tarter reckoned that decades of searching had amounted to the equivalent of dipping a drinking glass into Earth’s oceans at random to see if it contained a fish.

Once the numbers had been crunched, the researchers reckoned humanity has done slightly better than Dr Tarter suggested. Rather than dipping a drinking glass into the ocean, they say, astronomers have dunked a bathtub.

Huh. I wonder if that really is an apt comparison.