[This post was requested by b, who wanted me to write about the enduring popularity of Harry Potter. If you back me on Patreon for $5 or more a month, you too may be randomly selected to tell me what to write.]

Because something had to be.

This paper is one I find absolutely fascinating. The authors created an artificial music market: participants could listen to an unknown song by an unknown band, rate it from one to five stars, and optionally download it. The fourteen thousand (!) participants were divided into two groups, one of which could see how often the song had been downloaded by other participants, and one of which could not. The first group was further divided into eight “worlds”: participants could only see the downloads from their own world.

The results are perhaps not surprising. In the social influence condition, there was more inequality in which songs were downloaded: the songs that were most popular tended to stay popular. (The effect was larger when the songs were ranked in order of how popular they are.) The social influence condition also caused more unpredictability: the distinct “worlds” were far more different from each other than randomly selected groups of participants from the independent condition were. Assuming that rank in the independent condition is an accurate measure of quality, then success in each of the worlds is positively correlated with quality, the best songs rarely do very poorly, and the worst songs rarely do very well. But it was quite common for an objectively mediocre song to shoot to the top of the charts, perhaps because an early participant happened to like it, and this snowballed.

Of course, in the real world, social influence is a far stronger force than it is in this study. You could pretty easily listen to all 48 songs in the study, and no doubt many people did, but it is impossible to read every book published in the course of a year. In fact, most of the ways we choose books to read– other than, of course, serendipitously stumbling across an excellent book in a bookstore or library– depend on social influence: recommendations from friends, book reviews, awards, bestseller lists.

Quality is an explanation of why a book has an ordinary amount of popularity: for instance, the popularity of George R R Martin’s Sandkings is no doubt because it is a wonderfully chilling horror novelette. (Seriously, check it out.) But I don’t think he improved that much as a writer between Armageddon Rag (which was an utter commercial disaster) and A Feast for Crows (his first bestselling novel). And it is certainly not because of any virtue of Martin’s that A Song of Ice and Fire got adapted into an HBO show while, say, the Lilith’s Brood series did not.

(I am so mad at HBO. When I was in high school, I quit reading ASOIAF until it was done, because I didn’t want to reread four thousand-page books every half-decade when the books came out so I could remind myself who the fuck the characters were. “All I have to do is avoid Martin fansites until the series is over,” I said to myself. “It’s not like it’s going to be turned into a wildly popular TV show and I will have to excuse myself from conversations at parties lest I have the ending spoiled.” Ha ha bloody fucking ha.)

(This is the TV show watchers’ revenge for all the gloating I did about the Red Wedding, isn’t it?)

Anyway, Harry Potter is not normal popular. It is stupidly, wildly, amazingly popular. It is a mistake to judge a children’s book by the same standards that you judge an adult’s book, but even as a children’s book Harry Potter is solidly good-but-not-great: I would put it roughly in the same class as A Series of Unfortunate Events or Animorphs, not as good as the Time Quintet. And yet there is only one of these book series where, despite not having reread the books since high school, I am familiar with the names of two dozen minor characters. (Marcus Flint, Lavender Brown, Terry Boot, Blaise Zambini…) Normal popularity is easily explicable by quality. Stupid, wild, amazing popularity is due to luck.

I am not sure what particular set of events caused Harry Potter to become more popular than A Series of Unfortunate Events, or if it was simply a lot of people’s individual decision to recommend this particular book. But it is easy to answer the question of why they’re so popular now, which is because they have been popular in the past, and therefore there exist many people who want to recommend the series to others and read it to their children, and even those who haven’t read the series know whether they’re a Gryffindor or a Ravenclaw.