Isaac Asimov's three laws of Robotics are probably the single most highly revered set of rules for a fictional universe ever convinced. Before he started trying to connect the Robot universe to his other fiction they always were depicted consistently. They're so highly revered that other writers have used them as if they are just a given, from The Forbidden Planet to the Megaman games (in Japan).
This blog post isn't about that however. It's about the fact that Isaac Asimov did not pre-plan them, they were not in some secret Bible he constructed before he wrote his first piece of Robot themed fiction. He started just writing stories about Robots how he naturally felt inspired to write them. And then someone else, his Editor I think, told him "ya know your Robots seem to function on three basic laws" and then Isaac ran with it. This observation being made opened the door to stories he would never have written otherwise.
There is a common perception out there that serialized fiction always works best when the writer has everything carefully planned out in advance. Even though in the case of anything that has lasted more then one season or trilogy, that's never actually been the case, however much they may want their fans to think otherwise. These fans may admit it's unrealistic to pre-plan every scene of all 154 episodes of a 7 season show. But they think it's important to know where the show is headed, and to have a "Show Bible" that lays out all the key rules of the lore, even ones you're going to waits years to mention onscreen.
Some fans of the Wheel of Time series are obsessed with a belief that the books are still playing out according to some master plan the original author laid out decades ago. I have no idea whether or not that's true, I haven't read any of it yet. But I find it amusing.
If Joss Whedon refused to leave his original plan for Buffy Season 2, Spike would have died in episode 10. But Buffy wound up feeling like it could have been pre-planned, buy in it's closing seasons cleverly drawing on what came before. So basically I'm saying I do not think Joss planned for The First to be the final season's Big Bad when he wrote that Season 3 Christmas special, but it sure seemed to fit once that was how it played out.
The average person does not know that Alexandre Dumas novels were written in a serialized format. Among us who do know a perception exists that Dumas stories were more pre-planned then others. And maybe he tried to be that way, but given what I know about how that industry worked, there is no way he wasn't subject to editorial whims based on reader opinion. But Dumas and his rivals in that field like Paul Feval laid the foundations of modern genre fiction.
Telling a story that is carefully constructed from start to finish is of course often great. But that doesn't work for something ongoing. Madoka Magica was 12 perfectly executed episodes. Then they decided to milk it some more. If you want something to last years, it's best to allow it to be flexible.
Some shows seem to have poor endings because the creators wanted to stick to an ending they envisioned at the same time they wrote the Pilot, even though the show had evolved. Star Trek Voyager was a victim of this.
You may think "Mithrandir, isn't this odd coming from someone who seems to believe George Lucas about how pre-planned Star Wars was???". All I believe is that Vader was Lukes' father by the time A New Hope was filming, I don't care how many early drafts don't fit the final product we got. In SFdebris series about the development of Star Wars he delights in trying to refute the idea that Vader meaning father means something by going over these early versions. Yet Father-Son dynamics (with the father still alive) are all over these abandoned concepts he talks about. Darth Vader is several of those concepts merged together, and thankfully Lucas noticed that Vader means father at some point. To me the big proof of this lies in how Anakin is never mentioned in Vader and Obi-Wan's conversation, yet their backstory as presented to Luke revolved around Anakin.
Plenty of other things clearly did change. The Emperor was originally envisioned as just a puppet/figurehead according to the Novelization. Yet the Novelization also proves something like the Taxation Disputes with the Trade Federation was always part of the Republic's fall. I think Luke and Leia were already siblings when Empire was filmed, because it's ending makes no sense if they aren't, but I don't know about ANH.
So, my point is. It's about the journey not the destination.