There's an old joke among free-market types where one economist sees a $20 on the ground and delightedly bends over to pick it up. The other economist scolds him for the effort, saying, "If there really were a $20 on the ground, someone would have picked it up by now. It must be an illusion."
Today, I head to the Metro for the evening commute. There are two turnstiles to enter and one to exit. Yet there is a huge line of people behind one of the enter turnstiles while the other is vacant.
I reason: if the other enter turnstile was working, someone would be using it. So I write it off as broken.
After I've waited behind 8 or 9 people for the one good turnstile, someone walks by and gets through the "broken" one without incident. I follow behind, through the turnstile that's been there all along.
So much for rational markets ...