There are basically two types of stories to tell in the fictional world: ones that you intend to have a finale, such as in movies and most books; and ones that you intend to continue indefinitely, such as most comics, manga, and TV series. The latter kind presents an interesting challenge: how do you keep a story with the same characters going on forever?
Usually you resort to the Elastic Principle or the Scheherazade Principle.
The “Elastic Principle”, as you might guess, is analogous to a rubber band, spring, or anything that’s elastic. Such objects can be “distorted”, to a degree, and always return to their original shape so long as the distortion isn’t too severe. The same applies to plotlines that use the Elastic Principle:
“A plotline can only feature a dramatic change or development insofar as the conditions of the story are the same as they were originally at the conclusion of the plotline as they were in the beginning.”
In other words, no matter how bad things get during any given episode or plotline, by the end “everything has to be the way it was before”, so that if you were to watch the next episode or plotline following the current one before the current one, ideally you would not know you had ever gotten out of sequence. This principle is key to a great deal of children’s programming, who lack the commitment and sense of time to be able to process long, complex, and involved plots. It was also key for years in comic books or action genres, as it had the virtue that a new viewer or reader could ideally “start anywhere”.
On the negative side, these type of plots only work on shows for more child orientation, usually designed to sell toys, or for a limited duration. Eventually the series will become repetitive and suffer from a loss of drama, as the idea will become clear that nothing will ever “advance” and the characters will be fine after the arc. This usually leads to the authors resorting to more extreme plots and conditions to try to either create drama within the individual storyline or to give the impression that conditions will change, only to revert at the last moment. These usually involve Jumping the Shark or, in cases where the changes are too extreme, relying on a Cosmic Reset Button.
If a plotline relies on the Elastic Principle for more than five or six seasons, it usually is forced to incorporate some “permanent changes” of a small sort (i.e. new character, a single major life change for an established character), but this is not a total violation of the Elastic Principle as plotline changes are not continuous and the Elastic Principle is quickly restored.
The “Scheherazade Principle” gets its name from the main character of “One Thousand and One Nights”; who preserved her life by starting to tell a story to a king on one night but never finishing it, resulting in a stay of execution until after the next evening, at which point she would finish the story only to start a new one which she would also leave unfinished. The same idea applies to several modern series as well, and is summed up as follows:
“The last plotline thread of the series cannot terminate without initiating a new thread.”
Essentially, a series can indeed have plotlines that progress or advance, or even multiple ones on several storyline threads, but at no point can all of these threads be resolved. If down to the last thread, a new storyline must begin prior to termination such that the series never has a stopping point. The end result is a storyline that progresses and yet also never really “gets anywhere”.
These plotlines are far more long-lasting and dramatic in nature, and enable a story to span sagas and yet continue endlessly. As a result, they are typically more long-lasting than plots that follow the Elastic Principle. However, over time, they will eventually stagnate as well and fall victim to the same pitfalls of the first kind. When it becomes clear the overall story is not going to end, it too will result to Jumping the Shark and progressively more extreme situations to continue to kindle interest.
“The Simpsons” – This show is a clear example of the Elastic Principle after too long. Eventually, in later seasons, permanent plotline changes began to be made such as Barney quitting drinking after his character had been a stereotypical souse for over ten years, and Maud Flanders dying. However, the basic dynamic of the show is still the same. Interestingly, “The Simpsons” lampooned its own Elastic Principle as early as Season Five in “Homer Loves Flanders”, when Bart and Lisa broke the fourth wall to talk about the fact they knew something would happen to ruin Homer’s new love for Ned Flanders, and the Elastic Principle ended up being “forced” because while they were still friends at the end of the episode, Homer spontaneously hated Ned again for no reason at the start of the next one.
“Teenage Mutant Ninja Turtles” – The Elastic Principle. In the original cartoon series, Krang and Shredder would routinely hatch plans only for them to routinely fail. The one time their scheme succeeded was during their plot to repower the failing Technodrome, which ironically maintained the Elastic Principle in the opposite direction. Just as the Elastic Principle would be violated if Shredder and Krang ever defeated the Turtles, it would likewise be violated if the Turtles ever defeated Shredder and Krang.
“Transformers” and most 80s action cartoons – The Elastic Principle.
“My Little Pony” – The Elastic Principle. The original series does this, but the “Friendship is Magic” reboot is more debatable.
“Peter Pan and the Pirates” – The Elastic Principle. I point this one out because this show obeyed the Elastic Principle so closely that the plot was designated such that Peter Pan’s own reason for existence and mental well-being depended upon him constantly adventuring and fighting Captain Hook, but never actually triumphing over him.
Pretty much every Silver and Golden Age comic book – The Elastic Principle. Whether you prefer DC or Marvel, up into the 1970s most comic plotlines were always designed to be one or two shots, and at the end everything would be back to the way it was before, which is why classic comic book characters were so easy to pick up.
Bronze Age and later comic books – If they’re ongoing, they obey the Scheherazade Principle. Any given comic book you pick up typically goes a bit further on multiple arcs, adding a new one occasionally and terminating another on occasion.
Soap Operas – The Scheherazade Principle. Probably the most obvious and blatant example too, as soap operas are notorious for having some mystery or abrupt event happen at the close of a storyline to start a new one.
“My Little Pony: Friendship is Magic” – Progressively more the Scheherazade Principle.
“Supernatural” – The Scheherazade Principle.
“Pretty Guardian Sailor Moon” – The Elastic Principle. While there’s some inclination of the Scheherazade Principle, or even the fact that neither principle is obeyed because the series has a definitive ending, the fact of the matter is each arc is so similar to all the others that effectively it just repeats and resets, usually with a Cosmic Reset Button. The TV series was even worse with the Monster of the Week dynamic.