Second Season Downfall

The vast majority of television shows don't make it very far. Networks order dozens of new series every year, launch the most promising ones in the fall... and almost immediately begin cancelling ones that don't live up to expectations, replacing them with the shows that didn't make the first string of launches, in the hope of eventually getting a schedule of hits. This is the root of Too Good to Last: the network model simply isn't generous to shows that don't get off to a healthy start.

But for all the dozens of shows that fail in their first year, there are a few that survive this initial culling, complete their first season, and are renewed for a second. Smooth sailing from now on, right?

Well...not always. Sometimes nobody expected the show to make it, and so the writers and producers pulled out all the stops in the first year, leaving nothing to work with for the next season. Sometimes a show with a novel concept inspires imitators that either pull off the gimmick more skillfully, or are so ubiquitious that viewers become bored with both the original and the knockoffs. Sometimes Executive Meddling is to blame, especially if the second season coincides with a change in network leadership. Sometimes there's no clear cause at all; the show simply ran out of steam, and Seasonal Rot kicked in early. In any case, there are a lot of shows that make it through a successful first season, only to fall victim to a Sophomore Slump and get canceled by the end of a disappointing second season. In the end, these shows are Short Runners.

Compare Jumping the Shark. Contrast Long Runners.

Examples of Second Season Downfall include:

The Ropers, a spin-off of Three's Company, did great as a six-episode tryout on Tuesday nights following its parent show. But once it was moved to Saturday nights for Season 2, the ratings fell and the show limped through the year.
Joan of Arcadia, thanks to heavy Executive Meddling to make it more marketable to teens.
Twin Peaks. David Lynch explicitly stated that he never wanted to bring the Laura Palmer story to a close, preferring to use it as a frame for the sub-plots and span it over several seasons, but ABC didn't think the audience would stick around. As a result, her killer was revealed halfway through Season 2 and the show became nothing but sub-plots. It Got Worse when Lynch justifiably backed mostly out of its production to continue with his film career, directing only a few episodes with others directed by filmmakers of various skill levels.
CBS' expensive primetime soap Central Park West was heavily retooled after an under-performing Season 1, missing half the original cast. The retooling only alienated the show's dwindling fanbase, and it was canned at the end of Season 2.
Room For Two, an ABC mid-season replacement in 1992, overperformed in its short first season, ending as one of the top 20 shows on network television. Its second season saw its ratings plummet, though.
Dark Angel
Joss Whedon's Dollhouse survived its first season but was cancelled at the end of its second. Fans love to argue over whether or not Fox really felt the show deserved a second season, or were just trying to avoid a repeat of the situation with Firefly.
Heroes had an extraordinary first season, earning massive amounts of praise. The second season unfortunately showed a decline in writing, and the show never really recovered. There were so many retreads of past plots, and Season 3 seemed like a Random Events Plot that was extremely hard to follow, resulting in a mass exodus of viewers.
Glee is another example of a show that enjoyed a tremendously positive reception during its first season, earning praise from viewers and critics, making the cast members ubiquitous in ads and at award shows, and even prompting the TVLand Awards—put on by TVLand, a network which specializes in classic TV—to declare Glee a "future classic." Then came the second season, and despite the well-received introduction of Blaine, the writing started to decline. Quinn seemingly forgot all the lessons about friendship and kindness she'd learned in Season 1 and was back to being a vicious Alpha Bitch at the beginning of the season. Rachel went from being mildly annoying to being unbearably obnoxious (even tricking a potential singing rival into going to a freaking crackhouse to get her away from glee club auditions). And the show started to feel like one overly-long Public Service Announcement, as each episode become more Anvilicious than the last. Even the initially-welcomed introduction of Blaine and the Warblers started to go sour, as many fans accused them of being a Spotlight-Stealing Squad. The reaction to Season 3 has been mixed.
The Boondocks started with a groundbreaking, critically acclaimed, and award winning first season that tackled many social issues having to do primarily with race and politics and had excellent writing and humor. The characters each had their very own quirks that made them all enjoyable to watch and they each had a good share of screen time and development. Come season 2, and the entire show has been exaggerated into something else entirely. The characters have been massively Flanderized with their most annoying traits brought Up to Eleven, particularly Huey, who's supposed to be the shows main protagonist and narrator, but is severely Out of Focus with only one episode in the entire season focused on him(which, to add insult to injury, ended up getting banned), and has had nearly all the character stripped from him,going from being a wise, yet paranoid conspiracy theorist, activist, and angry black kid, to an almost emotionless, quiet spectator with nothing really to do or say. Not to mention the ridiculous amount of guest stars. the show became much more cartoony and frenetic, and at times seems to perpetuate the racial stereotypes it mocked in the beginning. Despite this its gone on to have a third season, and a rumored fourth one on the way.