In both cases it's a shift of direction, but I'll start with the latter example of romance because it's simpler. Before I explain anymore, let's address something: what is a story?
Character A wants something and something is preventing him from getting it.
How is a novel structured?
inciting incident -> rising action - > CLIMAX <- falling action <- conclusion
Basically, in the beginning, you introduce a conflict. In the romance story, that conflict is shyness. A good, logical story would have the character CONFRONT and SOLVE that issue on his own--when that happens, that's the climax. Such a progression would be the natural path of the story.
(Does that path sound boring to you? It does to me. That's because the conflict is extremely weak; it could never create a strong novel on its own. But that's an issue for another day.)
Often, what happens instead of the natural path of the story--because that story is very weak--is a plot device that sends the story spiraling into another direction. Something shoves the characters together, and shyness is no longer that much of an issue. Sure, it's still there, but the characters no longer have to approach each other. In furry fiction, this is usually the point at which they get together, make perfect first-time sex, and the story ends:
weak inciting incident -> weak conflict -> plot device -> climax (pun'd)
Now, it is possible for a plot device there to instead carry the story to a really strong position:
weak inciting incident -> weak conflict -> strong plot device -> strong rising action -> ...
This is what I call discontinuity syndrome--the story starts weak with a weak conflict, then a plot device sends it spiraling into a strong, tense work of fiction. Sometimes, you can do that on purpose and use it to your advantage, and you'll know when that opportunity comes. Generally, though, that's not what we want to do.
In my opinion, if you have a story that looks like the above diagram, you're starting in the wrong place. Start with the REALLY BIG CONFLICT that everyone wants to read about. You don't have to smack everyone in the face with it on the first page, but you really should open a book at a strong point, not a weak one. Work the weak conflict into the strong one.
For example, instead of having the characters meet each other, go gaga over each other, then get forced together, open the book where they get forced together. Their feelings could now be distracting them from the plot--that's a conflict, stronger than shyness, that produces tension and helps drive the story forward. Heck, maybe when the plot's at the climax and there's about to be a BIG EPIC BATTLE, that can motivate them to get together--or as I would do, have them break off.
Basically, what we DO NOT WANT is a Plot Device that shifts the focus of the story--meaning that it solves a conflict that the characters otherwise would've had to solve on their own. Honestly, why do it for them? You're killing your own story by nuking the tension.
There's a special type of plot device called a deus ex machina that's pretty similar to what I'm talking about, and I'm sure it's familiar to just about about all readers of fan fiction.
Deus ex Machina: a writer writes himself into a corner, and the characters can't resolve the conflicts on their own, so the writer pulls a god out of his ass and it solves the conflict for them.
More technical definition:
A deus ex machina is something that resolves the plot in place of the characters; the characters never solve X problem, because some outside force does it for them.
The classic example of a deus ex machina is "It was just a dream" syndrome, where something terrible happens, except it didn't. Or maybe something terrible is about to happen the protagonist, and someone arbitrarily saves them (I'm looking at you, Tom Bombadil).
Contrary to popular belief, deux ex machinae are not *all* bad, but most of them are. One that's really good is the one at the end of Basil's "Finding Time." There's one at the end of Hamlet, too. Just stick with my definition and never let a deus ex machina solve the major conflict.
For the record, though, you are given one plot device that you are automatically allowed to use to get the story going. It's my belief that the inciting incident should come from a plot device that sets the story on a certain direction--and it should stay on that same path the whole time. Of course, the characters might not always know exactly what path they're supposed to be taken, and that's fine.
And that leads me to the good plot devices. Yes, they exist! And if you don't use them, you are silly.
Let's take the imaginary novel in which the goal is for particle physicists to discover the Higgs boson (force-carrying particle that determines objects' mass). Let's look at the natural path:
inciting incident (someone predicts the Higgs's existence) -> rising action (physicists construct the LHC, a huuuuuuuge particle accelerator, and run into all kinds of problems along the way) -> CLIMAX (They find the particle!) <- falling action (Celebrations, awards...) <- Conclusion (The results are published.)
Since we know what a bad plot device is, let's examine a few:
1.) someone else finds it first;
2.) someone else proves that it doesn't exist;
3.) the LHC appears to lack the strength to detect the particle
Now let's look back at the natural path of the story. It's not bad, but I as a writer have a problem with it: it's too linear. I ask myself, "Who'd want to read that story?" and I don't get any answer besides "physics nerds!" From the very beginning, you can pretty much tell that they're going to find the particle. End of story.
Here's a trick to writing. People do not want predictable stories. They want stories that are predictably unpredictable. You can have them find the Higgs if you want, but I might choose to take a different path.
What if the particle collisions have enough energy to force open some of space's extra six dimensions? What if it creates a "bubble" of 9D space that researchers can enter? What if inside the bubble, they find not only the Higgs, but other particles that allow them to act in unheard of ways in the existing three dimensions? What if it allows them to write the equation of the universe?
I know it's physics-nerd science fiction, but it's the basis for good physics-nerd science fiction, if you do it well enough. The researchers could all agree to keep the unlocking of the universe secret, but maybe one of them could betray the pact and try to use new-found science to make himself into God. So the researchers not only have to stop the mad scientist, but also answer reports and provide fake test results for those who funded their research.
Those are the kinds of plot devices you want to use. As cliché as the last example sounds, it's much more interesting than a boring linear story.
But aside from those kinds of things, I just really dislike plot devices. iDunno.
