“Mad Men” begins airing the second half of its final season in April, and chances are you are due to be disappointed. Maybe Don Draper will topple out the window of a Manhattan skyscraper like the shadowy figure in the show’s opening credits, or maybe he will perish by more prosaic means. Maybe he will earn redemption, or maybe he will turn out to be notorious skyjacker D.B. Cooper. (Yes, that’s an actual theory circulating online.) Maybe the final scene will flash-forward through the rest of the twentieth century; maybe the screen will just fade to black. But the safest prediction about the finale is that it will make people very angry. Expect furious debates asking whether the show rewarded loyal viewers’ 80-something hour investment, or whether it wantonly betrayed their trust. It’s an outcome “Mad Men” showrunner Matthew Weiner has tried, futilely, to forestall. While the series began in 2007 with the intrigue of hidden pasts and switched identities, it’s never been propelled by a central question or mystery. When asked what viewers should expect from “Mad Men”’s end, Weiner has warned that the show will close on an ambiguous note: “My god, people must be prepared for that,” he told NPR’s Terry Gross in 2013.

If anything, the serialized television that has risen to the top of the cultural firmament in the last 15 years has prepared us for the opposite. The contemporary cult of the showrunner comes with its drawbacks, and one of them is the obligation to provide satisfying closure. “The Sopranos,” “The Wire,” “Breaking Bad,” “Game of Thrones”—these shows are densely plotted and narratively complex. Each episode is a link in a chain, filling in the puzzle but leaving the final picture unclear, and practically obliging us to tune into the next one. We sit riveted, lest we miss a clue. We wait for the big reveals—unless the whole season is available via streaming, in which case we binge, to hasten the payoff. We do not merely watch. We watch for the answers.

There are certain adjectives that the marketing people reach for when a big new show debuts. These series are bold. They are unconventional. But in fact, as a number of critics in recent years have noted (The New Yorker’s Emily Nussbaum, Huffington Post’s Maureen Ryan, and Slate’s Willa Paskin among them), a formula has congealed, and it’s one with a particular flavor. The protagonists are macho and morally compromised. These men (of course they’re men) are brilliant at their jobs, whether that’s cooking meth or selling ads. The signifiers of Important Television have become so rote that copycat series like Showtime’s “Ray Donovan” and AMC’s “Low Winter Sun” have cynically adopted the genre’s gritty trappings without any of the intelligence or ambition of their forebears. Strip away the recycled ingredients, though, and the thing that links every prestige release is that it takes the form of an ongoing narrative. These shows are—to borrow a fetishized term from another medium—longform.

But that’s very recent history. The most celebrated shows of television’s early years only offered standalone episodes. These 1950s dramas—“Kraft Television Theatre,” “The Philco Television Playhouse,” “Studio One,” and the iconic “Alfred Hitchcock Presents”—were the new technology’s most respectable offerings, culling the talent pool of the New York theater world to offer up inventive and often thought- provoking self-contained stories. (In the first half of the decade, before the perfection of videotape technology allowed production to move to Hollywood, the episodes were performed live.) The shows were popular among the kinds of middle-class households that could afford a television set, but also felt sort of guilty about tuning into low-brow entertainment such as “The Ed Sullivan Show” and “Dragnet.” Playwright Paddy Chayefsky wrote intimate, slice-of-life teleplays for “Television Playhouse” that he then turned into feature films. Gore Vidal wrote a “Goodyear Television Playhouse” episode about an alien visiting Earth. But by the mid-’60s, the format had been entirely supplanted by series with continuing characters. Intermittent attempts at revival failed. In 1985, Steven Spielberg created a sci-fi/horror anthology series for NBC and got Martin Scorsese, Clint Eastwood, and Robert Zemeckis to direct. It bombed and was canceled after just two seasons.

For the next two decades, most television dramas stuck with the episodic approach, following a more or less consistent cast of characters but efficiently resolving conflicts within the hour. The first big departure from that format came with the premiere of “Hill Street Blues” in 1981. Created by producer Steven Bochco, the cop show was the anti-“Columbo,” with threads of storylines connecting each installment. Other shows adopted the style within different settings: a hospital, a law firm, a group of married yuppies. By 1995, amid the rapture over “ER” and “NYPD Blue” (another Bochco hit), Charles McGrath was heralding the rise of the “primetime novel” in a New York Times Magazine cover story.