When I was an adolescent, an adult once told me that a period of two weeks was called a “fortnight” because that was how long people would stay in forts during a war in colonial or medieval times before being replaced with the next shift.
This is absolutely hogwash, of course. A fortnight just means “fourteen nights.”
But here’s the thing about that fact. It satisfied two essential elements necessary to make it a false but “sticky” fact. First, no part of my brain was immediately trained to reject it: it didn’t contradict any of my prior biases, it wasn’t tied to anything I was being asked to do, it didn’t register as automatically false. It slipped under my “skepticism radar,” and it would do the same for most people. Second, it made me feel kind of smart: “Oooh, look at this new cool little trivia fact I know, which I can maybe later use to impress other people.”
So this fact stuck around in my head for a long time. Since the “fact” was totally trivial, it lasted a long time without being disproven. Even if I went my whole life believing it to be true, that false belief would never have caused me to lose my job, make my health suffer, etc. And it was contagious, because if I told it to someone else, they were likely to have exactly the reaction I had when I first heard it.
If if’s false but trivial, who cares? Why bother considering this at all? Because it illustrates a weakness in our perception of the world. This piece of false information was both spreadable and persistent for reasons that can absolutely apply to information that is harmful. Just because this piece of information didn’t really carry any cost for falsely believing it, doesn’t mean another piece of information won’t. That other piece of information may just as easily fly under your skepticism radar, but also do a lot of damage once its inside your decision-making matrix.
For better or worse, we live in a world of massive connectivity of information. When I first heard the fortnight thing as a kid, I didn’t have Google in my pocket, on tap at all times. Checking the etymology of the word “fortnight” would have been an all-day project at best. Now, it’s very much worth it to take an extra fourteen seconds to run new information past a filter or two. Don’t let things just take up residence in your brain without your permission.