So, this is one of those tidbits that I had sort of recognized but never had actually seen called out until I read it in the late Blake Snyder's Save The Cat, but once I read it, I completely saw the logic to it. It goes something like this: when you watch a movie, it has a main plot (the "A Plot") which is what the movie is about. Defeat the evil overlord, let's say. But that won't be the only plot - there will be another story going on, usually a romance or coming-of-age sequence - which runs alongside the A plot. This "B plot" is the first big subplot of the movie, and it's rarely the last. There are usually several more subplots (C, D and so on) that might revolve around secondary characters resolving their own stories, and that's all well and good, but for the moment I just want to focus on the A and B plot threads to illustrate an idea.
There's an instinct to think of the B plot as chrome, or as something that's shamelessly added to appeal to a demographic. If the A plot is about space ninjas punching giant robots, then the addition of a romantic B plot can seem like a blatant way to try to sell the story to wives and girlfriends. And, heck, it can be that. I just saw Mega Shark vs. Giant Octopus this weekend, and in addition to being hilariously in its awfulness, it was a reminder that just because something has been released doesn't mean it did everything right.
The trick of it is this: the A plot is doomed, especially in adventure flicks. The hero can't overcome the villain, at least not the way he is when things start out. He's too busy whining about power converters or is otherwise lacking in what is necessary (resolve, skill, information or the like). The B plot is where he gains that thing he's missing. It may be as crass as finding out the weakness of the villain because he rescued just the right orphan, he might learn valuable lessons about life and friendship, he might find a reason to fight or it might be something else entirely. The exact details of this aren't important as much as the idea that the B plot provides the key for resolving the A plot.
With that realization, you then open up a better understanding of the role of other subplots. They may help the A plot resolve, or they may help the B plot resolve so that it, in turn, can help the A plot resolve. These plots are all threaded together like a series of slipknots - if you just tug on the A it will never come loose, but if you tug on them in the right order, it all just opens up.
While this may be unfamiliar language, the basic model here is something that most GMs are familiar with, since this is classic MacGuffin adventure model. The only way to kill the Dark Lord is with the Sword of Weeping Widows, but the only way to find the resting place of the sword is to as the Oracle of On'lev, but to find the oracle you need a map from the library of Farmount, which is currently in enemy hands. It's quite direct and linear, but it's a series of plot and subplots all the same. The A plot (kill the dark lord) requires the B plot (Get the sword!) be resolved, which in turn requires the C plot (Find the sword's location from the oracle) and the D plot (Get the map to the Oracle) to be resolved.
In the classic D&D sense, each subplot equates to a dungeon and it's a pretty solid model to provide a framework to tie together adventures, but I'm calling attention to the larger model because it suggests two ways you can improve the experience.
The first is simple and easy to implement - there's no need for these things to be purely linear - a given element may require two or three things to resolve it, which allows you to branch out and give players the freedom to explore things in the order they like. If, for example, the location of the sword was known, but the Oracle and the Library both needed to be checked to get it back, players could choose which one to pursue first rather than follow a dictated order. Yes, on some level this is just a bit of sleight of hand, but there is always going to be a balancing act between keeping adventures interesting and leading players by the nose, so when you can err in favor of giving them some leeway, you should.
The second is a little bit more of a stretch, so bear with me. One of the problems with a lot of classic adventures is the question of why the characters are the ones dealing with this. Certainly, well motivated characters have reasons that they might be taking action, and that works very well on a personal scale, but if you're talking the kind of heroic threats that are such a staple of gaming, there's a question of why someone who's more powerful, smarter and possibly better looking (that is to say, an NPC) isn't dealing with this problem?
This question is especially problematic in heavily populated published settings and level-based games. Certainly there are ways to make excuses for why no one is intervening but they get strained after a while. So with that in mind, the answer may be found in a B plot that is more like those found in the movies than in the usual module. When the B plot is just another adventure, then yes, anyone with the skill could resolve it. But when the B plot is tied to a personal issue, like a relationship between a PC and an NPC, then only that PC can resolve it. Now there's a reason it's his story, and not Badass McNpc's.
On some level this is just a reminder that plots need to be personal, but it's also a tool to help keep that from being too ham-handed. The temptation is to make the A plot personal, and that can get rough because there are only so many ways to tie a PC to the main plot that haven't been done to death. There can only be so many chosen ones or children of prophecy before it gets cliché. Making the B plot personal gives you a hook for players without it being so blatant. When a childhood friend is The Big Villain, that can work maybe once if you're lucky. If a childhood friend is a lieutenant for The Big Villain and I someone you can talk to? Less of a stretch, and opens much more interesting doors.
Plus, it helps the world hang together a bit better. If the PCs really are interesting (and they should be) they should have a network of friends and family, and it's only natural that those friends and family end up in interesting places. If your PC trained at the best military academy in the world, then OF COURSE some of his classmates are going to be recruited by bad guys - is the bad guy really looking to recruit the second best? Things like this let you reinforce the ways in which the PCs are exceptional by demonstrating that people who share an attribute with them are well regarded for it.
All of which is to say, next time you pull together an adventure, ask yourself what your b plot is, and how it matters to at least one of your characters.
1 - A wonderful book on screenwriting, one of my favorites.
2 - Yes, in reality, there are plenty of wives and girlfriends who would cheerfully pay money to watch space ninjas punch giant robots, but I think you understand my point.
3 - For less adventurey movies, this may be more subtle, but for action movies this tends to be pretty cut and dried.
4 - By which I really mean The Forgotten Realms, of course.
5- Including the ultimate "screw you" of "They're doing more important things". Thanks for underscoring what a bunch of useless chumps we are!
6 - One trick for this that doesn't show up in much fiction but is incredibly useful in gaming is the combinative element of the party members. One way to truly guarantee that the party are the only folks who could have resolved this is with each sub-plot keying off a different member of the party. Consider, the example of the school friend who's now an enemy general. The PC warrior has an in with him, but arguably so does anyone else from that school. However, if the second subplot element (say, his fondness to Ialantian artifacts) is one that a second PC in the group can address, then the set of people who could solve this problem has just dropped by another order of magnitude. In one sweep you've cemented the player's position AND acknowledged their backgrounds.
7 - This, by the way, is one of the greatest arguments for supporting color within a system. Combat abilities are nice in combat, but allowing characters avenues for external interests and connections makes for vastly better (read, less generic) plots.