(or "The Naked Engine")
This will actually be my 144th post on the subject of the "storytelling engine", and I've written all of these in the belief that there actually is an element of conscious design in creating an ongoing series, one that is different to that of creating a single story. Writers and editors have to create elements that can sustain a potentially indefinite number of stories, each one distinct and unique despite the ideas and themes that they share, and some things do that better than others. The job of creating a series is different than the job of creating a story, and editors of comics in particular need to keep that in mind even before the first issue is published.
Nowhere is this idea vindicated better than in 'Showcase', DC's Silver Age series that was essentially a try-out book for their new ongoing series ideas. Each potential comic got a three-issue run (or, on occasion, a three-story run within one issue), and editors decided based on the sales of those issues whether or not to green-light a new book. However, it's hard to imagine that sales numbers were the only factor, based on reading the various different comics that appeared in the first twenty or so issues of 'Showcase'. After all, the test-runs of different concepts served not just as a way of determining how well a book would sell, but also how easy it would be to write for. And some books have better storytelling engines than others.
The first issue, for example, was a comic about firefighters. The concept must have seemed commercial--little kids like fire engines, fighting fires is generally seen as a heroic activity with lots of danger and adventure, and you can create some pretty exciting tales out of it. However, the first issue contains three basic stories...fighting fires at a building, fighting fires at a circus, and fighting fires at...another building. Apart from the change in location, and the appropriate details about the firefighting techniques used in different situations, the concept was already starting to show its limits after one issue.
The Challengers of the Unknown, though, or the Flash, or Adam Strange all made repeated appearances in 'Showcase' even after it became obvious that they were popular and could sustain their own series. (Because no editor likes to take a concept that sells well and say, "OK, job done, let's hand off the great numbers this character is doing to someone else!" Not even when it's their job.) They've already been discussed in their various respective entries, but it's very much worth noting the way that each one has a protagonist or protagonists that are active and seek out adventures, each one has a supporting cast that has their own story hooks, and each one has a setting and a variety of antagonists that further assist writers in coming up with ideas. Not only are they popular, but any reasonably talented writer can look at Multi-Man, Iris West, or the planet of Rann and come up with a way that these elements can create a new dilemma in the life of Our Hero(es.)
Books like 'Showcase' come and go, depending on the fortunes of the industry. In the 80s, we didn't see many because the market was doing so well...a try-out book wasn't needed, because you could count on a large enough audience that would try out a new first issue that you could just put the book out there and see what happened. Nowadays, we don't see many for the exact opposite reason; the current market is appealing so strongly to nostalgia that they don't see much of a reason to put out a book featuring characters we haven't already seen in some form or other. (It says a lot that the closest thing we got, "DC Universe Presents", was sixteen issues of characters we'd already seen in the pre-Flashpoint DCU.) However, should the market improve slightly, the time might very well be right for another series like 'Showcase'. Because there are times when it's worth testing your engines before the rubber meets the road.