Imagine you have a series of books: Book 1 through Book 6. Do the stakes in book 2 have to be bigger than the stakes in book 1? The same question applies with each book in relation to the one before it.
I know you don't have to, but would it be best to do it like this? If not, then how can I keep the series from collapsing into a boring story?
There are two main mistakes that authors make when it comes to raising the stakes from one story to the next.
The first is that they either raise the stakes too quickly, or simply don't know when to stop raising them, and the result is that eventually they run out of room in which to escalate without things just getting ridiculous. And as you mentioned in the question, once you get to that point, it's very hard to dial things back again without your audience getting bored.
The classic example of this would be the Dragon Ball franchise. It started off as just the goofy adventures of a kid with a monkey tail. Then it started introducing antagonists that threatened to take over the world. Then Piccolo actually did take over the world. Then villains started showing up that were capable of destroying worlds, and again, they actually did so. Then they started facing off against literal gods that were strong enough to destroy the entire universe, and now (IIRC) they're fighting beings powerful enough to destroy the entire multiverse. Where do you escalate to from there?!
The second problem is that, more often than not, these newer, bigger threats tend to come out of absolutely nowhere, with no build-up or foreshadowing. Sometimes, this can work well and surprise both the audience and the characters, but other times, it makes it look like you're just pulling these new threats out of your arse (which, a lot of the time, is actually the case). I recall that one Tumblr post about Supernatural:
It's like, you beat the Devil himself? Well, now you've gotta fight the Devil's cousin Phil, who has conveniently gone entirely unmentioned up until now, but he's totally twice as evil.
[...]
That last paragraph was literally supposed to be the most ridiculous hypothetical example I could think of, and people are messaging me to say "His name was Metatron, not Phil". I can't even make fun of this show.
So how do you avoid those problems? Well, the first one can be avoided by making sure the stakes are raised gradually, and by mixing in more personal threats. For example, Book 3 might have the hero fighting to stop a villain from conquering the world, but Book 4 might have him fighting to save a loved one from a curse/illness/kidnapping/[insert crisis here]. For the world as a whole, the stakes are much smaller in Book 4, but for the hero, the stakes are higher because the threat is that much more personal.
The second is easy to avoid if you're planning all six books in advance, and can build up each threat before they appear, but what if your publisher suddenly asks you to write a seventh book? Then an eighth, and a ninth? You have to keep making up new threats as you go, and that's where this problem tends to creep in. You just have to try and make sure that each new threat is consistent with the world you've built up to that point, and that it makes sense that none of your characters have heard of it or mentioned it before. Dragon Ball, for example, is able to sidestep this problem by having its villains come from outer space, or alternate universes, or the future - of course Goku hasn't heard of the Androids, they don't exist yet!
This is often done, and it avoids later books having a sense of anti-climax. But it can feel artificial, and lead to later books being over-the-top.
It also depends on how closely the books are tied. Of they are really a single story, as the three books of The Lord of the Rings are then the overall story will usually have an overall climax, but the key stakes may be known early in the story, and remain the same. If the books are essential;y separate stories about continuing characters or in a continuing setting, then each book must have enough at stake to interest the reader. But there is no need to increase the level in each volume.
For example, in the Aubrey/Maturin series by Patric O'Brian, the degree of intensity and "amount at stake" go up and down several times during the 20 finished volumes, but many fans find all of the books of interest, adn in my personal view they never "collapse into a boring story" That is as much a matter of skill in writing as anything.
Similarly, many detective series have about the same amount at stake in each volume. The Hercule Poirot stories of Agatha Christie, or the Nero Wolfe stories og Rex Stout do not have ever-increasing stakes, but each series remained popular over many years and dozens of volumes. The same might vbe said of the more recent "Penric and Desdemona" fantasy series by Lois M Bujold. Many other series fitting this patter could be cited.
On the othe hand, some series do seem to increase the stakes with every volume. The early space-opera "Lensman" series by E.E. Smith is very much a case in point. But this may not be the best model to follow, depending on the nature of the series to be written.
The other answers here have done a great job answering your question. If you need to do more research, I would recommend looking up Spectacle Creep and Power Creep.
Spectacle Creep is when the writer tries to keep things fresh by making the problems and things that drive the plot flashier or more intense. As @F1Krazy mentioned Dragon Ball as a good example of this.
Power Creep is where characters tend to become more powerful over time. This tends to tie into Spectacle Creep. If the next guy the heroes fight is as powerful as the last guy, it can lose tension. Writers often get around this by changing the type of problem rather than the intensity. If your heroes fight monsters, don't have them just fight bigger monsters. Have them fight monsters that attack them in unique, interesting ways that the characters and readers can problem solve.
Not at all.
The other way to go is to use character development instead. For instance, give your main character several more or less obvious emotional wounds and then deal with them in turn throughout the series. Or have them deal with a really nasty wound in increments...
If you want to stay safe from having to write beyond the last installation as you've planned it, you could start with simpler wounds like a carjacking, and then bring heavier ones on stage that may do the late entry due to the main character trying to shield themselves from them, maybe even recovering lost memories. Or do the opposite and have them deal with snakes...
Or make the story give them wounds as you go. Who said a hero could withstand being shot at, kidnapped, and almost killed without getting emotional scars? Or what if they start to self-medicate to deal with space monsters, or whatever?
One example of character development is "Castle" where the stakes stay more or less the same throughout the show, while the characters evolve. Another example is "Buffy the Vampire Slayer". Here the stakes do change (up and down), but check out Willow's development! Check out Buffy's... that's at least why I'm a fan...
Update: Another way to keep a series interesting is to deal with emotional wounds and character development for different characters in a larger cast.
I recommend checking out TV shows that use the more classical approach to tell a mini-story in each episode. Those techniques can definitely be applied to writing a book series as well. (E.g. "Buffy the Vampire Slayer", "Chuck", "Castle").
I'm rewatching "Chuck" right now and "John Casey" is a nice example of a character that comes on the show as a simple, but funny character, and then, several seasons in, starts developing.
Not at all. As a kid, my father read paperback mysteries, about one a month. We had dozens of them, and I read them too. (some were sexy, but my father let us read literally anything in the house.)
Most of the mysteries were series; I think my dad had about 20 novels in the Rex Stout's Nero Wolfe series. And they were all a long series, the same people in and out of the detective's life, but the stakes were always pretty much the same. Catch the dangerous murderer. Unravel the misdirection. Escape attempts by the murderer to kill you. Date the love interest. The long backstory might change, but for the most part there were no big arcs within the Nero Wolfe series. The mystery plots were uniformly good and different, the same plot was never used twice, the same twist was never used twice.
You can see this in some episodic TV, as well. It is common these days to introduce some long arcs in a series, but many are static. M*A*S*H ran for eleven seasons and Hawkeye Pierce was pretty much a constant irreverent, joking, angry-at-war brilliant surgeon. Radar stayed pretty much the same throughout. And it was on 11 seasons because the audience loved it!
The problem with escalation is escalation. You go from saving a village, to the country, to the world, to the universe. A static series, like a mystery series, or adventure series (think Indiana Jones), can go on for as long as you can keep writing. that is true in fantasies (like the TV series Merlin). In Harry Potter, the escalation was in the age and expertise of the students, but the mysteries were largely self-contained. Rowling was in no big hurry to solve the mystery of Harry Potter's survival. She wrote until (I presume) she got sick of it; each book a new mystery. Harry and the crew could have easily graduated to Hogwart's professors and still had more adult adventures, but I am guessing Rowling wasn't into that. Her genre was children's fiction, and as her crew aged (and her wealth grew) I think she just lost interest in their progression into adulthood.
I could note the same lack of (or extremely slow) lack of escalation and progression of characters in Star Trek (any of the series). Many sitcoms have very little escalation or character growth.
(Typically, if you start seeing escalation after several years of a series, the producers and writers are trying to rescue declining ratings.)
If it is possible for your series, I'd very much recommend just writing another rousing but completely different adventure with the same cast of characters. They can certainly learn a lesson within a shallow character arc (just like the characters in Star Trek or sitcoms). Just make sure you aren't writing the same book again; come up with a NEW adventure, not something your previous readers will recognize as a rehash of your first plot with the names of villains changed.
No, they don't. Indeed, that's one of the biggest mistakes writers tend to make. People don't care if you don't escalate from adventure to adventure, as long as you challenge your characters in a different way that is still entertaining. Indeed, having these lower stake arcs that challenge the characters in out of the box ways are a useful way to deflate tension and reset the stakes between big escalatory conflicts where escalation is the point (e.g., Marvel's Infinity Saga is an example of the latter).
Here's one good example: Jojo's Bizarre Adventure. Jojo is infamous for the fact that it just keeps going, and it almost never does the same thing twice...even when it resets the universe. Part of the strength of that is the story switches characters every part, but that might be considered cheating since it's almost an entirely new story. So I'm going to focus on Parts 3 and 4, which include a couple of overlapping characters and thus tend to be more connected.
Part 3 ends with the big bad of Jojo dying in an epic confrontation to save the world. It's built up as this grand finale and everything. So how do you continue the story from there? The big bad is not brought back to life, and arguably never is aside from Part 7 for spoiler reasons. Instead, Jojo goes the complete opposite direction and has a low-stakes arc of a bunch of teenagers goofing around trying to solve a mystery in Morioh, and the villain isn't some overpowered vampire but a certain 33 year old who wants to live a quiet life. This is despite the fact that Part 4 had the protagonist of Part 3 as a supporting character and he was just as OP there as he was at the end of Part 3.
However, because the plot is so totally different from Part 3, it works, and it resets our expectations and stakes for the second major arc that covers Parts 4-5-6.
No.
Mystery series can go from book to book with the same old stakes of determining the murderer.
Conan the Barbarian can have adventure after adventure in which he saves himself and any confederates from the story peril. I particularly note that sometimes he saves kingdoms and sometimes he saves himself, and the stories were intermixed in publication order. Sword & sorcery, in fantasy, particularly allows random adventures.
Romance series revolve about the romance every single time.
One thing to be wary of is character development. If you want a long series, it's better to either omit it or switch characters. Romance novels, of course, end when the hero and heroine have their Happily Ever After; rather than undermine the character development a new hero and heroine have to emerge. It is possible to have a character arc that covers several books, but if you drag it on too long, it loses its forward motion. And if you have character development, it is unsatisfactory for the character to stop growing as the main character.
No.
Case in point: the Discworld series starts with avoiding the end of the world, and moves to less dramatic and more local subjects, occasionally coming back to potential end-of-world scenarios.
There are already very good answers here; I'll try to give a slightly different POV just as an addition to them.
You say it's a series of books telling one big story; in this case, the stakes don't necesarilly have to be "bigger" each time, but they do have to move the story forward, making sure each step takes both the characters and the readers closer to the big bad final threat of the final book.
Do note that this doesn't mean that the stakes cannot be higher everytime; this completely depends on how the story develops. Some authors actually decide to have the previous to last book end with a big cliffhanger where everything seems grim and hopeless for the heroes, so they already "lost" and the last episode/chapter/part is not about facing the biggest threat but to recover from already facing it.
As long as you don't run out of "higher stakes" early in your story, or as long as (for example) book 3 doesn't feel more dramatic and climatic than book 6, you can still rise the risks and dangers your characters face.
Raising the stakes simply isn't necessary to tell a better story, for several reasons.
So I'm challenging your frame: making a story have higher stakes than the last story is a trope/gimmick/whatever you want to call it. It's not bad, it's a fine thing to employ. Tropes are useful things and no writing can escape using some tropes. But they are just tools, options. No trope fits every story. And tropes aren't what make stories great.
Great answers already, but I wanted to give another example of a series that handled fluctuating stakes very well (in my opinion at least): the Gotrek and Felix series of the Warhammer Fantasy universe.
The books have stakes that vary greatly from one to the other. In some they might be up against a large horde of barbarians, dragons or other monsters, that threaten the lives of thousands, if not millions, of people. In others it's about a more personal struggle, like a loved one being turned into a vampire or being captured as slaves.
So in some books, they defend the lives of countless people, while in others, if they were to fail, nobody would know or care. Yet it is the last kind, that are the most interesting, because of how personal it is. In the first kind, they have to keep going, because otherwise the world as they know it might be destroyed (or at least part of it). In the second, they could give up at any moment, without there being a larger impact, but they won't because of their personal investment.
More examples: Animorphs, a popular series for middle schoolers in the 90s ran for 54 mainline books with only scant few having continuity between books that mattered for order they were read in. It was largely able to work in comedic plots with very serious plots. For example, a book introducing a race of aliens hell bent on universal conquest... and standing at a height of 1/16th of an inch tall followed a book where one character learns of his true parentage and has to play off the shock when the big bad guy of the series tries to manipulate this all while questioning the hero is questioning his own humanity. It was preceded by three books that dealt with a traitor in their hero's ranks. An earlier book (Number 8) holds a theme of "Humans through Alien's eyes" following two rather dark books. Book 17 the heroes learn that Maple Ginger Oatmeal is a kryptonite to the bad guys and is proceeded by an "Internet Chat Rooms are scary: 90s edition" and followed by a cosmic horror story.
Harry Potter's Third Book is the only one which does not directly feature Voldemort, and follows Book 2 (arguably the darkest of the first 3 books) and is followed up by Book 4, where Voldemort finally returns to full power, and then the series gets dark as it progresses.
Shows that had season "Big Bad Evil Guys" like Buffy The Vampire Slayer actually had very threatening villains that were followed up by weaker ones the following season. Post season 3, the show almost seemed cursed as the the even season's villains were not all that compelling or threatening compared to the prior season, while the Odd number season baddies were much more beloved (Season 4's Adam had the tough act to follow of The Mayor from Season 3, Season 6's characters were nerds out for power and were barely a threat to the heroes (not helped that they followed Season 5's Glory, who was the most physically powerful character the heroes had to contend with ever) whose plans backfired and the heroes had to spend several episodes trying to save them. Season 7's villain was kind of lack luster when compared to the contenders for best baddies but still had cool tricks and played psychological war quite well, but season 6 had so little to redeem it to begin with.).
Other series that are anthology in nature and thus the stakes from one to another don't matter because the stories of the book are self contained. For example Twilight Zone can feature William Shatner seeing Gremlins out the window on his plane's wing... Aliens that wish to serve human kind... for dinner... and a dictator condemning a man for continuing to hold the profession of "Librarian" and believing in God, both practices which the State has determined to be obsolete. Vastly different stakes (individual, to a crowd, to the entire world) and all three fondly remembered as some of the best episodes in the series.
