Tink Thomson on The Umbrella Man in Errol Morris’ short film:
The only person under any umbrella in all of Dallas standing right at the location where all the shots come into the limousine. Can anyone come up with a non-sinister explanation for this?
It does seem weird. People will naturally ask themselves informal questions such as “could that just be a coincidence?” We can make the question increasingly formal:
What is the probability that the only person in Dallas holding an umbrella would be standing where the President was shot?
Or even better:
If we were to randomly place the Umbrella Man in one of the locations where a person was standing along the parade route in Dallas, what is the probability that he would end up right where the President was shot?
You will notice that our minds turn a retrospective observation (“hey, there was a guy with an umbrella standing next to the limo. That’s weird.”) into a prospective randomization question (“if we randomly place the Umbrella Man…”).
We are only asking about the probability of the Umbrella Man standing there, because we already observed that he was standing there. The observation drove the question.
I suspect that had the President been shot in a different location, we would have identified someone in the crowd that did something that seemed too weird to just be a coincidence. That’s part of the reason why conspiracy theories are so seductive — there is always some observation that is hard to explain with chance.
I have made this point before, but this example is better than the ones I came up with.