IT HAPPENED to Heroes, which went to zeroes in double-quick time before being cancelled. It happened to Lost, which lost a large chunk of its audience midway through the second series and left those that stuck with it feeling cheated by a lame "they were dead all along" finale.
And now it's happening to Glee. The backlash, I mean. What seemed new and vibrant last year, buoyed by a cast of fresh, largely unknown young faces and a dollop of knowing, grown-up humour guaranteed to keep the adult audience interested, suddenly looks stale, cynical and nakedly commercial.
It's now all about the high-profile guest stars (Britney Spears, Neil Patrick Harris, Gwyneth Paltrow), the themed episodes (The Rocky Horror Show, the Madonna special and a planned one based on Fleetwood Mac's album Rumours) and the inevitable spin-off albums (too many to count).
I missed some later episodes of the first series of Glee, as well as last week's second series opener, but I've seen enough -- and heard enough from two of my daughters, one of whom has given up watching it out of a mixture of boredom and frustration -- to know something has gone wrong.
Having sat through last night's episode, one weary eye on the TV screen, the other on a curiously slow-moving clock, I reckon I could have missed it, too, without missing much.
Centred on St Valentine's Day, it was a flimsy, repetitive excuse for the cast to belt out romantic standards, many of them so heavily auto-tuned they made The X Factor sound like a pub singalong recorded on a Dictaphone.
Glee has stalled. It's stagnating. The storylines are going around in ever-decreasing circles. To be honest, this on its own wouldn't be too much of a problem.
Plotting has never been Glee's strongest point. The fun has always come from the characters.
But the characters have stalled as well. Kurt (Chris Colfer), an empowering figure for most of the first run, has morphed into a tired gay stereotype, mooning and moaning his way through it. "It's so nice to be around girls for a change," he sighed last night, snuggling up like a pink teddy bear between Rachel and Mercedes.
There wasn't even a single sighting of acid-tongued Sue Sylvester, the only presence that kept many of us watching through the leaner episodes, to relieve the tedium.
The merchandising monster may keep it steamrollering along for another couple of series, but the joy has gone from Glee.
In 2009, documentary film-maker Andrew Tait made a fine programme called Trouble in Amish Paradise, which revealed the supposedly gentle community immortalised in the movie Witness to be every bit as complex and treacherous as any society.
At the time, Ephraim Stoltzfus, his wife Amanda and their children were about to be excommunicated from the Amish church and shunned by the community for espousing more traditional Christian beliefs (the Amish Bible is written in impenetrable Old German).
In the low-key, melancholic Leaving Amish Paradise, Tait caught up with Stoltzfus family, now members of the fundamentalist Charity Church -- which many Amish claim is little more than a cult -- and struggling to make it in the wider world.
Ephraim wanted to devote his life to preaching, trusting in God to provide for his family. God didn't deliver, however, and he ended up having to find building work.
Another couple, Jesse and Elsie, and their children had also been excommunicated and hooked up with Ephraim and his new church. Jesse is naive at best, dim at worst. Ephraim, on the other hand, is humourless and hard to like.
You couldn't escape the feeling that they'd simply traded one oppressive culture for another.