It goes like this: When six and seven appear together in print, or in speech, or on television, or in a YouTube video, or even just when you write them down on loose-leaf paper, that’s “six-seven.” “Six-seven!” you say, you probably being a middle-school-aged child. Such is the youth phenomenon known by this name. Now you know, but chances are you already did, especially if a preteen has lived in your house anytime since this spring.

Six-seven-ing seems to have peaked around Halloween, and now, as the holidays descend, its days are numbered. My own 11-year-old never liked it (a culture of contrarianism pervades the Bogost residence), but now she actively scorns it. “The memes will reset on New Year’s Day,” she recently announced. I hear the same from other parents of kids her age. Worse, parents are now saying “six-seven” (as are sports leagues and fast-food chains), which is of course fatal for anything kids find cool. But six-seven might have been doomed by design. It just wasn’t built to last, not as a staple of kid-dom anyway.

People have referred to six-seven as a meme, but that’s not a helpful way to understand it. Yes, the tic spread widely, starting in March, thanks to a few popular online videos, but what doesn’t spread online these days? Better: Take six-seven as an example of “childlore,” a name for folk culture that arises or spreads among children. Jump-rope rhymes such as “Mary Mack” are childlore, as is doggerel slander such as “Fatty Fatty Two-by-Four.” So is the concept of cooties, a fictional disease caught when someone gross touches you. Likewise the “Cool S” doodle, that squared-off figure that looks like a vertical, pointy-ended infinity symbol; paper fortune-tellers (aka cootie catchers); the soothsaying paper-and-pencil game MASH; playground rituals (“No take-backs!”); and received superstitions (“Step on a crack, break your mother’s back”).

Childlore thrives when two conditions are met. One is a murkiness of origins. Nobody knows who first folded a cootie catcher or drew a “Cool S.” Some childlore feels like it has always existed, stretching back into eternity and reproducing itself as legend. Other trends arrive as if air-dropped by aliens. This doesn’t bother kids, because everything is new for them. Learning an arbitrary playground ritual or a chant for the numbers between five and eight is not much different from discovering that red pandas exist, or how to plot points on coordinate planes, or that Goldfish crackers also come in pretzel flavor. The 10-or-so-year-olds who latched onto six-seven did so just because it wormed through their ears into their brain and then departed out of their mouth.

But obsessional online culture has sought to answer questions of origin rather than waving them off. Anything can be researched and explained today, whether as historical fact or invented conspiracy. Doing so misses the point. Six-seven supposedly originated in a Skrilla song, but knowing that fact offers no further understanding. To trace a children’s phenomenon to its explanation also ruins it. Who cares where it came from? For kids, the point is that it is here, and it is theirs.

The second condition is a network. Adults may construe a child’s life as unencumbered, but kids actually have very little control over what happens to them. They thrive or wither at the whims of teachers, parents, and other adults who control their hours and days. Within those constraints, childlore offers kids an opportunity to develop and control a local culture. Another kid teaches you the jump-rope rhyme. You watch one draw a doodle and then do it yourself. Six-seven started this way, and then it circulated through the tender, sticky hands of children.

Alas, what started in their network soon became a social currency for adults online. Gen Xers and Millennials—the parents of today’s middle schoolers—couldn’t leave six-seven be; they’re accustomed to burning through such memes like their parents or grandparents did cigarettes, as if culture writ large can withstand habitual abuse. Social-media-influencer culture also latched onto the phrase for their own attentional ends, as did brands, the indefatigable scavengers. These forces stole six-seven from the kids who had nurtured it.

But six-seven’s fragility is just as much a product of its structure. The numbers have no meaning of their own. Six-seven is just a lasso looped by fate around two adjacent integers on the number line. It hides no secret payload of violence, sex, sacrilege, or anything whatsoever. This emptiness surely helped six-seven’s rise. Hearing it might irritate parents or teachers, but that irritation has no cause and therefore merits no reproach. What are you going to say—Stop naming whole numbers? (Some schools have said just that.)

Some successful forms of childlore—like bubble-shaped handwriting, or the way to fold a notebook page into a note for passage to a friend—were more resilient because they were material, and bounded by circumstance. They had to be inscribed onto or made from paper, for example, or to arise in particular social contexts. Six-seven just floats loose. It can be uttered for any reason or for no reason. My older daughter, who is in her early 20s, admitted that she recently found herself saying “six-seven” involuntarily upon hearing a co-worker refer to “six or seven” of something. Like one must say “cow” upon seeing a cow along a roadside, prior knowledge of six-seven demands releasing its utterance when numerically provoked. “I didn’t put my heart into it,” my older daughter said. “But what’s important is: It wasn’t a choice. It just came out of my mouth.” Six-seven was so universal by nature that it was bound to spread into the world of adults, which suffocated it.

Teachers, parents, and even some kids are pleased to welcome six-seven’s end. “No one really says it anymore,” a friend’s 9-year-old reports; my own kid longs for this report to be true. Others are more circumspect. It’s not dead but “slowly dying,” according to another friend’s preteen daughter. “No offense, Mom, but parents don’t understand,” she added. Instead, both kids explained, their peers have started saying “41”—a competing meme that carries six-seven’s ghost (six times seven, plus six, minus seven)—as if to mourn it. Six-seven’s end brings relief, but also sorrow: Childlore, a staple of boy- and girlhood for centuries, has become tenuous and fragile. Being a kid is hard, and it isn’t getting any easier. Even the silly trappings of youth now feel as fleeting as everything else.