When I was a shaver, I believed there was a creature called Bigfoot, and I could support this belief with evidence. Many cultures have stories of a shaggy-haired man-like reclusive creature. Many reputable people say they think they have seen or heard such a creature. There are blurry photos and videos that show what looks like Bigfoot. Scientists have found footprints in the snow that are too large to be made by any known animal. And so on.
When sceptics argued my evidence might have another causes, for example pointing out that the freezing and thawing of ice can make the footprint of a bear or wolf much larger over time, I was unmoved, because my theory explained all the evidence I could see.
But then someone smart asked me a question: “Where is Bigfoot’s poop?”. I saw the logic immediately. Given that Bigfoot is large and uses lots of energy roaming widely in the forests, he needs a lot of calories to keep going. That means he must eat a lot. And as he is a humanoid, he presumably excretes the remains of his meals. He himself may be reclusive, but his poop wouldn’t be. So why don’t we find his spoor as we do that of every other creature? Does he carry it with him in an American Tourister bag or something? This point shattered my faith in Bigfoot.
Psychologist Daniel Kahneman’s marvelous book Thinking Fast and Slow well describes the basic cognitive limitations that made me (and many other people) believe in Bigfoot. The first is the tendency to see common themes where they aren’t any, which made Bigfoot seem to me the logical, essential thread connecting all my disparate “evidence”. The other is that the human mind focuses on what is in front of it while being poor at accounting for what is not present, like Bigfoot’s poop.
Whoever asked me the poop question (I wish I could remember so that I could thank him or her) didn’t try to dispute the evidence which I thought supported my theory. Rather, they took my theory as correct and then pointed out that what followed logically from it was not in evidence. Some people cannot be argued out of strange theories for emotional reasons, but those who can are more likely to be susceptible to this style of counter-argument than they are a direct attack on their observed evidence.
These thoughts were triggered by a passenger next to me on an airplane recently telling me that there is a new documentary coming out that will prove that TWA Flight 800 crashed into the ocean after leaving New York City because some terrorists in a boat shot it down with a shoulder-fired missile. I am not going to watch this film, but I can guess that it will assemble all evidence consistent with that theory.
There will be credible people on screen saying they saw a bright ray of light over the ocean right before the crash. There will be former intelligence officers saying that terrorists have always been interested in downing planes, and indeed that a terrorist cell in Africa even tried this once with shoulder-fired surface to air missiles. There will be someone who works at the NYC harbor saying s/he saw two suspicious guys in a rowboat, maybe adding that one of them was eating falafel or reading the Koran.
It will all be true and therefore seem compelling as long the viewer doesn’t exert the significant cognitive effort it takes to redirect their attention to what they cannot see, namely the evidence that would be present if the theory were true: If terrorists did it, why haven’t they done it again and again since? Given that terrorists want people to be afraid, why didn’t they announce that they did it? When the mind is directed to these questions, the plausibility of the theory shrinks to nothing.
As I said, some people hang on to conspiracy theories no matter what for emotional reasons, most typically because it makes them feel important to think they see the hidden truth that escapes all the suckers around them. But if you are arguing about TWA 800 terrorists or any other such theory with someone who is emotionally stable enough to appreciate logic, don’t argue about what they can see but what they can’t.