In most cases, when a TV show is a breakthrough hit, the plan is to keep it on the air for as long as possible. A good example of this mind-set can be seen in AMC Networks' (AMCX -0.60%) "The Walking Dead," -- it's not only gearing up for a spin-off, but also has its producers talking about a 10- to 12-season run despite the fact that the show's fifth season hasn't even aired yet.

This isn't necessarily the case with Time Warner's (TWX) HBO, however. A prime example is the subscription channel's "True Detective," which was one of last year's smash hits. While casting rumors are flying about season two (none of which are apparently true, by the way), show creator Nic Pizzolatto recently dropped a bombshell about the show's third season: it very well could be the show's last.

True problems
The issue with "True Detective" has to do with its unique storytelling approach. Instead of following a core cast over several seasons, each season tells a specific story that features its own cast. This is part of the reason for the buzz about the second season -- fans can't wait to find out who will be picked to follow the outstanding performances of Matthew McConaughey and Woody Harrelson. Unfortunately, it also brings the problem of having to start with a clean slate each season.

Not only does this mean that a significant amount of casting and pre-production work before each season, it could cause a disconnect with fans. Comcast's (CMCSA -0.37%)(NASDAQ: CMCSK) NBC learned this the hard way when season two of "Heroes" began with a focus on a primarily new cast. Amid other problems (not the least of which was the writers' strike, which caused part of the plot to be gutted to get the season into production), fans had a hard time connecting with and caring about the new cast after the explosive first season finale.

While "True Detective" isn't an effects-heavy show like "Heroes" was, it also won't have the advantage of popular characters from the previous season carrying over to continue their stories. As Pizzolatto put it to the Calgary Herald, "Every season, I'm essentially creating a brand new TV show. It can't have any growing pains like a regular first season. If it works, it has to work right out of the box."

The three-season limit
This constant restarting is the reason that Pizzolatto gave for the show being unlikely to continue on indefinitely. He described the annual restart as "incredibly exhausting," especially given that he was also writing every episode. He added, "I can't imagine I would do this more than three years," which would put the third season as the show's last (unless he changes his mind by 2016).

This isn't necessarily a bad thing. Since HBO is a subscription-based channel, it doesn't have to rely on advertisers and hit shows to bring in a constant stream of income. That's the reason that hit shows on standard networks keep going as long as they're popular, after all ... people are watching the shows, and advertisers are paying a premium to buy ad slots during those shows. With HBO that pressure isn't there, so it can be more selective with its shows and when to retire them.

Will 'True Detective' really end?
Three seasons of "True Detective" could work out well for HBO. While the show wasn't included in the channel's deal with Amazon.com (AMZN -1.64%) that made a number of HBO shows and specials Amazon Instant Video exclusives, three years of "True Detective" would be a good starting point to expand that deal. Given that the first season wouldn't appear on Amazon until 2017 even if it had been part of the deal (since seasons of current shows were scheduled with a three-year delay before being available for Amazon customers), HBO could offer the series in its entirety to sweeten the pot for any future deal extensions.

The show would also still have value to HBO in the form of DVD and Blu-Ray sales, which is another solid source of revenue for the company. Solid disc sales for its shows is one reason that HBO isn't overly worried about excessive piracy for popular shows like "Game of Thrones" -- sales figures show that even the pirates are still buying physical copies once they become available, so "True Detective" could still earn money even if it goes off the air.

In the end, HBO would gain more by keeping its showrunners happy and retiring popular shows like "True Detective" at a point when they can go out on top than it would be forcing the show to continue until audiences are no longer drawn in.