“AMC sold the show to Netflix early, so when people started talking about it, it was there for the watching,” said Alexia Quadrani, a media analyst at JPMorgan.

Last Thursday, I visited Josh Sapan, the chief executive of AMC Networks, at his office across the street from Madison Square Garden. You might expect him to be celebrating his zombies’ success, but you’d be wrong. Mr. Sapan has been at AMC for 25 years and he is too superstitious to tempt the gods like that. As a collector of lightning rods — he has acquired more than a hundred, two of them on display in his office — he knows that sticking out has a cost.

“I would have put big odds against a cable show winning over network five years ago,” he said. Still, he warns, “People’s taste in what is popular can be very fleeting and short-lived. There is some alchemy at work here that is hard to diagnose and replicate.”

“It’s a big moment to those of us who are in the business,” he added, “but I don’t think the general public, especially young people, even think about where programming comes from.”

The zombies have not devoured all Mr. Sapan’s challenges. Even though advertising in the fourth quarter is up 16 percent over the previous year, earnings at AMC fell short of Wall Street estimates because of a costly fight with Dish Network and expensive outlays to service debt.

And he’s right to give the American audience, a notoriously fickle bunch, a wide berth. Ask NBC, which went from first to worst this season in nothing flat. As my colleague Bill Carter pointed out, the peacock was on top of the pile in 13 of 15 weeks from September to December, according to Nielsen. Since then, it has dropped below not only its broadcast brethren but also Univision, the Spanish-language network.

“The Walking Dead” was actually NBC’s for the asking in 2011. At a news tour for television reporters in January, Kevin Reilly, who is now at Fox but was a top programmer at NBC when the show was still up for grabs, talked about the one that got away.