The phrase was in an episode of The Office prior to that. I think it's fairly old.

Not sure how long the subreddit has existed but I always assumed it was inspired by the episode of The Office where Michael asks Oscar to explain what a surplus is like he's 5. The broader usage on social media and the ELI5 shorthand are definitely the result of the subreddit though.

This article is definitely abusing the terminology, because I wouldn't expect even tech-knowledgeable people to know what Nostr is or does.

It’s way older than Reddit, it’s older than the Office. I remember Denzel Washington saying it in some movie when I was a kid, and I doubt it originated there. Doesn’t Einstein have a quotation about it, too?

I remember someone saying it in high school back in the late 90s or early 00s.

Are you smarter than a five year old, kinda show

"If you can't explain it to a six year old, you don't understand it yourself." - Albert Einstein (allegedly :))

I always thought that the quote was with "5 year old" and that it was the reason for ELI5 :)

In this article, it's just an AI-generated TL;DR, tagline, sub-title box that was badly prompt-engineered and the website owners didn't care about its quality. I am pretty sure the entire website is an AI generated news aggregator.