In discussing the challenges of writing serialized shows with a couple other writers/directors/showrunners around the table, we were talking about the changed expectations that have come about in the last decade or so. We're all old enough to have begun our careers in a more episodic time, when the process was suited to the content: The writers would move one episode at a time along a conveyor belt, from concept to index cards ("beats") on the board to outline to first draft, then hand it off to production and turn their attention to the next script in the sequence. This works great for episodes with standalone A-stories and minor internal histories to weave in along the road from ep 1 to ep 22 (because yes, 90% of the shows I have worked on had 22-episode seasons, not the now-standard 13).
But these days, the 13 episodes tend to tell not 13 stories (or 12 with big 2-part finale), but one story, broken across 13 hours. Instead of climax and revolution at the end of a given episode, false resolution of a single issue comes midway in the hour, followed by the set up of a new escalating problem, and episodes end on the kind of cliffhanger that used to be an Act Break.
I don't think the underlying stories are that different, in terms of how the characters are tested and put through their paces. But the structure is different. The 25 or 30 index cards that would once have been the skeleton of, say, episode 5, are spread more thinly across the canvas of the season, with those beats stretching from episode 3 to episode 7, with maybe a foreshadowing card back in episode 2. Meanwhile the cards from other stories, that in the old system might have been sequestered as episodes 6 and 8, are interspersed and overlapping and co-mingling. It starts to look less like a grid of neat lines of cards, and more like a word cloud or like this image of Verified Twitter Connections:
Which all seems completely reasonable, if you have the luxury of breaking all 13 stories on 13 whiteboards, and then swirling the index cards around like marbleizing a batter. But you don't. You only have a few weeks of writing before filming begins. You know the overall arc of your season-long story, but you only get to fill in the detailed beats of the first episodes before cameras start rolling. That means that you're filming what would have been Act One of the old-school episode 5, which is now scattered throughout episode 3, without having written Act Three. By the time you're wrapping up that story a few weeks later, you're already filming the beginning scenes of what would have once been a stand-alone season finale.
As one of the dinner companions said, it's like weaving a tapestry from the bottom up, without any reference art. You're making feet -- hopefully finely crafted feet -- without having mapped out the rest of the image. You know, or think you know, what the faces are supposed to look like, but you don't have a Weaver's Draft to keep all the threads on track. And that doesn't even take into account the midstream course-corrections -- whether organic to the story, or arising from external forces -- that mean somebody's knees are going to take a weird-ass bend to get them where they need to be.
This is when experience gets tested. Because when you have to make your best guesses on incomplete information, it helps to have been through it before.
This is also where a lot of TV veterans quit to go write novels, where you can have the unbelievable luxury of writing the last chapter before publishing the first.