As I may have mentioned before, my Advanced Fiction professor talks a lot about active protagonists. We hear the phrase "who is driving this story?" about three times per class. It's pretty valid, really, given that we tend to edit three stories per class (after finishing the scenes at the beginning of the semester), and many of our stories need that question to be asked of them. In the past, I've had some trouble with this, but I think I've finally really got it, so I feel like sharing.
The first thing that gave me trouble is obvious: like most rules, this has exceptions. Not every great story is driven by its protagonists. When our professor first told us this, someone immediately asked about The Great Gatsby; you could tell the professor was waiting for it. Yes, passive protagonists can sometimes be done well, but in some ways, they're actually more difficult. You have to give them a reason to be present at all the important scenes (because your story will be a real letdown if you never see the good stuff, and that's assuming people can even understand it). When a protagonist drives the story, he/she is almost always present, because these things would not happen without him/her.
What stumped me for a long time is that being physically active does not an active protagonist make. You can have a character who never stops to catch her breath, but who is still not driving the story. If all she does is react to others or follow instructions, she's not being active. Your protagonist must be why the story happens. This is what threw me, as I think of many stories as centering around a conflict or problem usually caused by the villain, not the protagonist. For example, detectives do not cause the murders they investigate, yet the story could not happen without the murders. Good guys, I argued, do not start fights with the bad guys. The bad guys start fights - and thus stories - because they're the bad guys.
I finally found one question which simplified things enough for me to really get it: Whose story is this? In the case of The Great Gatsby, the story is Gatsby's, though the POV is not. Usually this is not the case. Even in stories wherein the protagonist is essentially reacting to another character or event, the story quickly becomes defined by the way in which the character acts. Think of The Hobbit: the story starts with Gandalf and the dwarves telling Bilbo to do something. Does this mean that Bilbo has no hope to be anything but reactive? Of course not. Whose story is The Hobbit? If we put aside the title and even the point of view, it's still Bilbo's story. Let's say the book was written from Gandalf's point of view, or that of one of the dwarves - pick one. Would it make the story belong to that person? No. It would be Bilbo's story with a strange - one might even say poor - choice of POV character. At best, it would be a fantastical Great Gatsby; at worst, confusing and boring. (Can you imagine all the scenes wherein Bilbo would have to explain how, while the POV dwarf was wandering in the woods/hiding in a barrel/etc., Bilbo was off doing awesome things which advanced the plot? Besides, what about things about which Bilbo doesn't immediately tell his comrades? It would just appear later: "Oh yeah, and I have this magical ring.")
This is also, in my opinion, the best reason to change POV. Of my four longer works, two have included POV changes, both written in third person close. Rabbit and Cougar alternates between Rabbit's POV and Cougar's, switching at every chapter. Although I wrote it years before this class, I noticed that the chapter length varied based on whose point of view seemed most important at the time, especially toward the end, when the two spend some time separated. Since Rabbit and Cougar travel together for most of the story, that covers the "will he be there for the important scenes?" pretty well, but I think it's best to write the POV of the person most integral to those scenes, if that viewpoint makes sense to use. The person with the highest stake tends to make an interesting POV. For Lord of the Dark Downs, I switched between seven viewpoints. Yes, it's a lot, and it worried me at times. However, the times I had the most trouble were those when I found the character I was writing was not the one most heavily invested in the situation. Happily, since I wasn't doing any sort of pattern, I would then just rewrite that section for the point of view of a character whose motivations in the scene were more interesting to me. This means that some characters' points of view appear more often than those of other characters, but I think the story benefits, and I don't think any one character has so little to say that he or she should be taken out.
Anyway, I just thought I'd share that because it helped me see some things more clearly.
My website has not gone up yet. I will note when it does. It's still pretty exciting to me! :)