Now how to I learn something from it as a writer? I'd like to think I've learned that no series of mine should ever have an open-ended number of books. Never, never, never. To my eye, that way lies far too many dangers. Planning a series arc is the only sure way to keep from venturing into shark infested plot waters. Each of my series to date is a limited run with a specific beginning point and ending point. I'd like, someday, to get to finish a series. . . I swear one is within sight.
I want to acknowledge, however, that just because I will DNF a series that exceeds my muttered 'oh come on' limit - it doesn't mean there aren't other readers out there in the world feasting on that entire series. It pays to remember that when a publisher tells you they won't keep publishing your series - if your story isn't done and, like me, you really want to complete the arc of the series, you don't have to listen to the voices that tell you to just let it go. You can write your complete series arc, tuck it away, and then, when your rights revert, presto. Series. It helps if you know you have readers who are waiting for the rest of the story, but you're also allowed to write it just for your own satisfaction. Who knows. Maybe it will be a case of if you write it readers will come. Either way. Not everything in life has to have a return on investment.
Still. The only thing I know is that I really don't want to write a series that jumps the shark. But it may be necessary. Just so I know where that darned shark is lurking.