Every show, regardless of genre or format; regardless of idea or characters, has a shelf-life. No show can possibly exist forever and be as successful or as good as they were when they first began. Furthermore, most shows actually go through their best years very early on, within the first five seasons.
That is why it’s really important that any show knows its boundaries. Every show creator should have an exit strategy, an idea of how they would want the series to end. An ending that could, within reason, happen at any time, and definitely happen at the end of season five. This serves two purposes. A show will have direction and focus and never feel tired or worn-out and it means that a show never gets stale or changes to such a point that it doesn’t resemble the original series anymore.
The major issue is that no idea can go on forever without losing quality or running out of ideas. Even shows that have interchangeable cast, for example ER or CSI, reach a point where nothing new is really happening. There are only so many ways to investigate a murder or to treat a patient. Even the backstories of the characters become very similar, each person bringing with them some unknown baggage that gets revealed and affects the main thread of the series. This isn’t a bad thing, but does become very repetitive when a show reaches season 7.
That is even more the case when a show has a very unique, central idea. Prison Break, 24 and Lie to Me all have a unique edge that makes them stand-out. Prison Break is the tattoo blueprints and the excellent planned escape of the first season. 24 is the groundbreaking, real-time, shocking story and events and Lie to Me is the catching of criminals by reading their expressions. Unfortunately, these have a short impact and don’t have the same, unique effect when you reach later seasons. Luckily for Prison Break, it ended at season 4, Lie to Me was cancelled at season 3 (for that very reason I imagine) and unfortunately, 24 is trying to continue.
One show that highlights this issue even further is House. The first two or three seasons are fantastic. The cases are interesting and the characters are compelling. Unfortunately, past season four, the best season of the whole series, the show becomes formulaic. You can tell the pattern of the show, when the case will be cracked and sometimes guess how the side story will trigger House’s revelation. It was lucky for the show creators that House and his colleagues are such good characters that you kept coming back to watch their lives, and the medical cases became the side stories instead.
That’s not to say that a show can’t have a good season past five, it’s just that I don’t know of any shows which have their best season that far into their run. Friends, one of the longest running sitcoms, peaked earlier than five seasons. The Simpsons, the longest running show on tv, is way past its best, which could be found in the first five seasons. Both those shows continued to be watchable past season five but why keep making or watching television that is past its best?
If you stick to the five seasons rule, you will have a long enough run to tell the stories, flesh out the characters and develop key, interesting and expansive stories, without over-stretching or out-living your quality. You also get the chance to end a show before it becomes something only vaguely resembling what it was at the beginning, for example, Smallville.
You can also prove this rule by its successes. Three of the best shows on television ended before or around their fifth season. The Wire – five seasons. Sopranos – Six seasons (but best is with in the first five) and Breaking Bad (ending on its fifth season.) All these shows have concrete, well-rounded, focused stories that never seem like padding and still feel as authentic and quality as the first ever episode. Could you imagine the quality continuing into a seventh or eighth season of The Wire?
Overall, I don’t know of any show that is good enough, original enough or innovative enough to last more than five seasons and maintain its quality. Five seasons offer enough time to create characters, story and world’s that are entertaining without then beginning to stretch the shows credibility or capability. Imagine how much better your favourite show would have been had it stopped at season five… or worst, how bad your show would have become had it continued past five seasons.