Too many, too much
There's a problem I've noticed cropping up more and more often lately, in the way some authors first develop and then over-develop their plots and subplots, allowing both them and their characters to proliferate beyond the ability of mere mortals to keep track of them all, until the whole edifice starts crumbling under its own weight. It's most common (and most noticeable) in multiple-viewpoint stories, particularly those that have an ensemble cast dealing with complex plots and subplots.
The advantages of writing a fat, complicated, multiple-viewpoint, ensemble-cast book are many: they're popular; they provide both writer and reader with more than enough variety to keep from getting bored; they are in many ways a truer reflection of the complexity of real life events than something more straightforward would be; the variety that an ensemble cast allows for means that more people will find someone they're interested in and want to follow through all the adventures in the book; the multitude of viewpoints lets the writer show all sorts of cool stuff that would otherwise be behind the scenes; etc.
The trouble is that most of those advantages can very easily become disadvantages if they're handled even a little bit clumsily - and the more viewpoint characters and subplots the writer has to juggle, the easier it is for them to let things get ever-so-slightly out of balance. Which is all it takes to annoy a sizeable subset of readers.
A few years back, a friend who was working on her first big multiple-viewpoint book got six chapters and eight viewpoints into the thing, and then stopped and took two of the viewpoints out. All of her first-readers screamed bloody murder; we liked those two people, and we thought the scenes they had were great. My friend was adamant, however - and perfectly correct in her decision. Those two people weren't close enough to the central story she wanted to tell, and leaving them in would have thrown everything off-balance.
Or, to put it another way, whenever a character is the viewpoint character, the story is about them. It doesn't matter if the character is the cab driver whose only importance is that he drove Our Hero from Kennedy Airport to a hotel downtown; while he's the viewpoint, he's the center. And he's the center of his story, which, to him, is much more important than anything else that's going on in the book.
This means that in a multiple-viewpoint book, each and every viewpoint character has to be chosen with great care. This is particularly true when the writer intends to have a cast of five or ten people who are all meant to be "the main character" in some way - that is, a classic ensemble cast. It can be very hard to identify exactly which characters are at the heart of the writer's story (each of them is, of course, at the heart of his or her own…which is the fundamental problem).
A story told from a single viewpoint, whether it's first-person, tight third-person, or the sort of limited omniscient that still only follows one character around, has built-in protection against subplot proliferation. The reader can only see and find out what the single viewpoint character sees and finds out, and there are only so many things that one person can reasonably be involved in. The kind of multiple-viewpoint book that has a strong core plot or theme also doesn't usually tend to have problems with subplot-and-character proliferation; the strength of the main plot through-line keeps everything else from going too far astray.
The real trouble comes when the author lets him or herself be distracted by shiny minor characters and/or interesting bits of business that "might develop into something." Because the minute that cab driver gets his own viewpoint scene, his story is the one the writer is telling. And it's always, always fascinating and fun and interesting, because people's stories always feel that way to themselves, and when you're writing from the viewpoint of a character, you see their story they way they see it. And next thing you know, the caper novel about the ensemble cast trying to rob the Metropolitan Museum of Art has this whole involved subplot about the cab driver's romance with a police detective (see, the writer says to herself, it's relevant! There's police involved!).
And then the cab driver's family come into it, and there are more interesting complications there, and pretty soon the original caper novel is practically buried under the cab driver's cousin's drug smuggling subplot and his sister's angsting over whether she'll get into art school (see, the writer says desperately, Art! And they're planning an art heist! So it's, um, thematically relevant!) and the police detective's difficulties with precinct politics.
I've learned the hard way that any time I start justifying the presence of a scene, character, viewpoint, or general Cool Bit Of Business, it almost certainly doesn't belong in the story. If it belonged, I wouldn't have to do any justifying. (Saying confidently "That's setup for the problem with X that they're going to have three chapters from now" is not justifying it; saying "But…but…but it's relevant! Because there's, um, important stuff in this bit!" is a dead sure sign that I'm going to need to cut, and the sooner, the better.)
When I notice myself slipping into this pattern, I find it helps to snip the scenes to a file, and promise myself that I can write that other story later. Because that's the thing that's so seductive - all those fun, fascinating stories that aren't the one I'm telling right now, but that could be shoehorned in with just a little work… Promising myself that I can write a whole book about them and do a proper job of telling their stories, instead of giving them just a corner of this one, is what keeps me from falling victim to Endless Subplot Proliferation Syndrome. Most of the time.
