As it turns out, the powers that rule HBO operate in ways no less mysterious than those of the murky world of its recently canceled series, “Carnivale.” Yes, that’s right: “Carnivale” is dead, even though HBO won’t publicly admit it, and even though their decision reflects just how far the once-mighty cable channel has slipped from dominance in the year since “Sex and the City” and “The Sopranos” ruled Sunday nights. The final episode of “Carnivale” – a mish-mash of breathtaking imagery and confounding storytelling – demonstrated just how little HBO has learned about television from the shining examples set by the medium’s greatest masters.

To put it simply: At the end of a series that has kept millions of faithful viewers riveted and fascinated, you don’t just throw up your hands, walk away, and explain absolutely nothing. Shame on HBO for allowing “Carnivale” to conclude with an episode as deeply unsatisfying as “New Canaan, Ca.” (which will air again this Friday, April 8 at 11 p.m., if you want to see what I mean). The episode answered no questions whatsoever for its loyal, if dwindling audience. “Carnivale” left us hanging like no series of comparable quality in the history of television ever dared, and this deserves to remain an ugly blotch on the reputation of HBO (and the show’s creator, Daniel Knauf) for years to come.

Critics devote far too much time to assessing the beginnings of shows, when what defines their success – or failure – is how they end. Imagine your dissatisfaction with a literary critic who marveled at the opening pages of a Ian McEwan novel and then stopped reading, or a theater reviewer who left “Democracy” at intermission. But the unfortunate yet pragmatic reality of television is that writers never know how long their time-slot leases will last, and they write confusing cliff-hangers each season in the hope that they will force the landlord’s hand to keep them on for one more year. This results in good shows that never properly end, since greedy executives care more about consistent ratings than well-executed wrap-ups.

Yet for those who love television and relive its highlights in memory (or, nowadays, on DVD), the best shows remain those whose creators cared enough to craft a provocative conclusion. No one who saw it will ever forget the exquisite final episode of “St. Elsewhere,” the groundbreaking 1980s medical drama that wrapped itself with the revelation that the entire six year series had taken place in the imagination of a child. The final group hug of “The Mary Tyler Moore Show” offered emotional closure. (The cosmically hilarious sight of the MTM cat logo flatlining, after the closing credits, will never escape my memory.) Even the last episode of “Gunsmoke” – its 623rd – invoked a logical plot point of a landlord driving the Cartwrights off their property.

No such solutions were provided to the viewers of “Carnivale,” many of whom had studied the show’s 24 episodes to deconstruct its epic battle of good versus evil. Hints of the Holocaust hovered over recent episodes. The Dust Bowl drama’s two main characters, Ben Hawkins and Brother Justin, were established clearly as a selfless faith healer and an evil priest. But who were these people? It never became clear who Brother Justin (the dark preacher played with consistent flair by Clancy Brown) really was, nor were we ever told the true meaning of the battle between him and Hawkins.

Instead, loyal viewers of “Carnivale” were treated to spectacular but inexplicable images of cornfields and Ferris wheels and midgets and tattoos. It offered an addictive melange of characters and settings seen nowhere else on television, and worthy of our attention for that reason alone. But for those of us who fantasized that the season finale might introduce some explanations at last, our hopes were dashed by the death of Brother Justin in the darkness, both literal and figurative. The metaphors were left meaningless, the conflicts unresolved. Off the carnival went to another town, another place – with new questions raised that will now never be answered.

Why did HBO choose to abandon its “Carnivale” audience with so little consideration? It reflects, in part, a legitimate business decision: The series never caught on with a wide-enough audience to justify a third season. But on a deeper level it demonstrates HBO’s ongoing myopia with regard to programming – its mistaken belief that an audience will flock to whatever shows it wants to give us, whenever it feels like it. Its hubris in refusing to officially announce the death of “Carnivale” is symptomatic of HBO’s superiority complex: why bother explaining anything to an audience who’ll watch whatever we shove their way? The runaway success of ABC’s “Desperate Housewives” (a show about one-millionth as good as the worst show on HBO) serves the cable network right. It ought to be delivering “The Sopranos” on a reasonable yearly schedule, and it ought to own Sunday night. I don’t care what kind of a genius David Chase is – HBO should never have indulged the selfish need of the “Sopranos'” creator to skip off to France and leave us in the lurch for years, waiting for the next episode of the best series on television. HBO’s willingness to let “Carnivale” creator Daniel Knauf to slink off (reportedly to Showtime) without resolving his show’s multitude of mysteries was another blunder by a network that is rapidly losing its luster.

Maybe HBO’s motto defines its dilemma: If only it were television, and not some self-indulgent repertory showcase for writers who don’t know how to finish what they started, its audience would be growing, not shrinking. The growing failures of HBO represent a creative loss to the medium itself; it is incumbent upon the channel’s leadership to learn from its recent mistakes – and to reward its audience of intelligent, faithful viewers with shows that know how to end as compellingly as they begin.