WINKLER: ...I knew how to [water ski]. And my very short German parents would write me letters, and they would say: Tell the producers you know how to water ski... You could tell them that you could do this. I finally showed the producers the letter as a joke.
SAGAL: Because, wait a minute, your parents were, like, worried. You were the star of the most successful sitcom on television, and they were like, but maybe you can get a little more money if they know you can... Maybe he can make a success of himself if he can just water ski.
WINKLER: If I water ski, I will have it made in the shade.
...
SAGAL: All right, so you show the producers. This is back in the '70s. You show the producers the letter from your parents. Hey, I can water ski, you point out to them.
WINKLER: Yes.
SAGAL: So they come up with a story in which Fonzie has to water ski over sharks, over a tank of sharks?
WINKLER: Yes, I did. Well, I jumped over a shark. About that time, a guy named Jon Hein, who now has a radio show.
SAGAL: Yeah.
WINKLER: He was sitting in his dorm room with his good friend, and they came up with the expression, jump the shark.
SAGAL: Right. Because they decided that "Happy Days" at that point started to be less good, shall we say, than it used to be, and they said the moment when "Happy Days" started to go downhill is when Arthur Fonzarelli jumped the shark. And so jumping the shark became this universal phrase for the moment when something starts to go bad.
WINKLER: Yes.
SAGAL: How does it feel then to be the person who enacted now the single most important cultural indicator of impending decline?
WINKLER: I would like to say proud.
Not My Job segment of Wait, Wait, Don't Tell Me, Sept. 10, 2007