Internet virality works in very mysterious ways. If you needed further reminder of that, behold the improbable story of this quote:

The line, according to long-standing Internet legend, comes from the book “Paper Towns,” an earlier novel by John Green — the author of “The Fault in Our Stars.” Accordingly, like much of Green’s more quotable work, it’s been memed, sketched, illustrated, collagedhand-lettered, imposed over artsy out-of-focus photos, printed on luggage tags, printed on T-shirtstattooed on actual bodies, and generally reproduced on blogs and Web sites the Internet over. Green himself sells a poster of it in his online store: Until recently, text on the poster attributed it to him.

Except — as Green confessed on Tuesday, in a charmingly honest YouTube clip — the sentence never appears in “Paper Towns.” It never appears in anything Green has ever written.

“I suppose instead of blindly assuming I’d written something the Internet said I wrote, I should’ve done some research,” Green confessed in the video, which has been watched nearly 300,000 times. “[But] how many of us have failed to fact check something on the Internet? Most, I would think.”

The quote’s real origins, it turns out, are far more interesting. Several years ago, a then-13-year-old girl named Melody Truong wrote the somewhat-melancholy musing on her now-defunct Tumblr, “The Perfect Mistake.” Because Truong often quoted Green, and because she often posted quotes she’d illustrated, Tumblr users reblogged the sentence and began to attribute it to “Paper Towns.”

From Tumblr, the quote — and its misattribution! — spread to Pinterest, to Etsy, to travel sites and personal blogs. Green became so accustomed to seeing the quote that he simply assumed it was in the book he’d written seven years before. Then, one of Truong’s friends posted about the incident in a copyright forum on Reddit, accusing Green of “accidental plagiarism.”

“I stole it!” Green admits in the YouTube video. “I am the thief!”

To make amends, Green’s store is now splitting profits for the poster between Truong and the artist who illustrated it. And Truong, a self-described “amateur artist,” is also selling her own work there.

This is all very cute and funny and good for Truong, of course — she wrote on her new Tumblr that she’s “paralyzed by happiness” — but it also tells us something powerful and weird about the changing nature of authorship and identity.

See, Tumblr does a booming trade in inspirational phrases like these; there are even sites that generate this sort of shareable, sepia-toned quote meme. Obviously, each of these quotes was written by a single person, often expressing something keenly felt about herself. But in the process of sharing, the original author is cut out and only the words circulate, superimposed on an array of (likewise uncredited) images. Without the author, the quote speaks for anyone and everyone who reblogged it. It’s at once a deeply personal and deeply collective thing.

Green sees it differently: This is a perfect example, he says, of “how screwed up credit and sourcing and copyright are on the Internet.” But that might not be entirely fair. Today, when you search Truong’s quote, you’ll find it as a million memes — unattributed, authorless, belonging not to Truong but to the community. It’s a uniquely modern mode of self-expression, and one that media theorists are only just beginning to study.

“The new collectivized idea of the author celebrates the kind of creativity that comes from selecting, from accumulating a pastiche, a patchwork, a sample of others’ work,” the anthropologist Susan Blum wrote in a 2008 essay about how the Internet has challenged the idea of “authorship.” “The line between creation and what ‘copyright fundamentalists’ regard as theft is now completely — and consciously — fluid.”

In fact, there’s nowhere it’s more fluid than on Tumblr, where millions of people maintain personal blogs that consist largely of other people’s work. Even five or 10 years ago, a teenager with a blog would “express” herself by writing about her day, like in an old-school diary. Now a kid with a Tumblr can curate a kind of personal identity solely by borrowing from other people and reblogging Tumblr memes.

On Truong’s current Tumblr right now, for instance, there’s a close-up photo of a butterfly, several moody shots of romantic European houses, and a bit of graffiti that says “we still have to change the world.” None of these things were made by Truong herself. But by putting them together, they become hers. Who cares who wrote the graffiti originally?

“What is the self?” Blum asks. “What is the relationship between the self and its words? What are the relationships among selves? How does technology affect human interaction? How does technology affect the ways in which people engage with texts?”

(… I mean, are we talking people I know, or people I’ve never met?)