Sometimes a single word or phrase is enough to expand your mental toolkit across almost every subject. “Averaging argument.” “Motte and bailey.” “Empirically indistinguishable.” “Overfitting.” Yesterday I learned another such phrase: “Summer of the Shark.”

This, apparently, was the summer of 2001, when lacking more exciting news, the media gave massive coverage to every single shark attack it could find, creating the widespread impression of an epidemic—albeit, one that everyone forgot about after 9/11. In reality, depending on what you compare it to, the rate of shark attacks was either normal or unusually low in the summer of 2001. As far as I can tell, the situation is that the absolute number of shark attacks has been increasing over the decades, but the increase is entirely attributable to human population growth (and to way more surfers and scuba divers). The risk per person, always minuscule (cows apparently kill five times more people), appears to have been going down. This might or might not be related to the fact that shark populations are precipitously declining all over the world, due mostly to overfishing and finning, but also the destruction of habitat.

There’s a tendency—I notice it in myself—to say, “fine, news outlets have overhyped this trend; that’s what they do. But still, there must be something going on, since otherwise you wouldn’t see everyone talking about it.”

The point of the phrase “Summer of the Shark” is to remind yourself that a “trend” can be, and often is, entirely a product of people energetically looking for a certain thing, even while the actual rate of the thing is unremarkable, abnormally low, or declining. Of course this has been a favorite theme of Steven Pinker, but I don’t know if even reading his recent books, Better Angels and Enlightenment Now, fully brought home the problem’s pervasiveness for me. If a self-sustaining hype bubble can form even over something as relatively easy to measure as the number of shark attacks, imagine how common it must be with more nebulous social phenomena.

Without passing judgment—I’m unsure about many of them myself—how many of the following have you figured, based on the news or your Facebook or Twitter feeds, are probably some sort of epidemic?

Crime by illegal immigrants

Fraudulent voting by non-citizens

SJWs silencing free speech on campus

Unemployment in heartland America

Outrageous treatment of customers by airlines

Mass school shootings

Sexism in Silicon Valley

Racism at Starbucks

Now be honest: for how many of these do you have any real idea whether the problem is anomalously frequent relative to its historical rate, or to the analogous problems in other sectors of society? How many seem to be epidemics that require special explanations (“the dysfunctional culture of X”), but only because millions of people started worrying about these particular problems and discussing them—in many cases, thankfully so? How many seem to be epidemics, but only because people can now record outrageous instances with their smartphones, then make them viral on social media?

Needless to say, the discovery that a problem is no worse in domain X than it is in Y, or is better, doesn’t mean we shouldn’t fight hard to solve it in X—especially if X happens to be our business. Set thy own house in order. But it does mean that, if we see X but not Y attacked for its deeply entrenched, screwed-up culture, a culture that lets these things happen over and over, then we’re seeing a mistake at best, and the workings of prejudice at worst.

I’m not saying anything the slightest bit original here. But my personal interest is less in the “Summer of the Shark” phenomenon itself than in its psychology. Somehow, we need to figure out a trick to move this cognitive error from the periphery of consciousness to center stage. I mustn’t treat it as just a 10% correction: something to acknowledge intellectually, before I go on to share a rage-inducing headline on Facebook anyway, once I’ve hit on a suitable reason why my initial feelings of anger were basically justified after all. Sometimes it’s a 100% correction. I’ve been guilty, I’m sure, of helping to spread SotS-type narratives. And I’ve laughed when SotS narratives were uncritically wielded by others, for example in The Onion. I should do better.

I can’t resist sharing one of history’s most famous Jewish jokes, with apologies to those who know it. In the shtetl, a horrible rumor spreads: a Jewish man raped and murdered a beautiful little Christian girl in the forest. Terrified, the Jews gather in the synagogue and debate what to do. They know that the Cossacks won’t ask: “OK, but before we do anything rash, what’s the rate of Jewish perpetration of this sort of crime? How does it compare to the Gentile rate, after normalizing by the populations’ sizes? Also, what about Jewish victims of Gentile crimes? Is the presence of Jews causally related to more of our children being murdered than would otherwise be?” Instead, a mob will simply slaughter every Jew it can find. But then, just when it seems all is lost, the rabbi runs into the synagogue and jubilantly declares: “wonderful news, everyone! It turns out the murdered girl was Jewish!”

And now I should end this post, before it jumps the shark.

Update: This post by Scott Alexander, which I’d somehow forgotten about, makes exactly the same point, but better and more memorably. Oh well, one could do worse than to serve as a Cliff Notes and link farm for Slate Star Codex.