These days, it’s common parlance for TV fans to talk about a show “jumping the shark” when it starts declining in quality, usually due to some unexpected plot point or storyline. The origins of the expression date back nearly half a century, to the Happy Days episode “Hollywood, Part 3,” which aired on September 20, 1977 — the episode in which Henry Winkler’s Arthur “The Fonz” Fonzarelli accepts a challenge to jump over a shark while waterskiing. The episode has long baffled fans — but as it turns out, one of classic TV’s oddest moments was set into motion by Winkler’s father, who insisted his son tell producers about his waterskiing skills.

For some fans, including comedian Jon Hein, that episode was the beginning of the end of Happy Days. Hein popularized the phrase “jump the shark” through his website of the same name, after recalling a college discussion with friends about when shows started going downhill, as he told Michigan Today in 2016. During that chat, Hein’s roommate said, “When Fonzie jumped the shark.”