Completing a long story vs moving on to something new and shiny

Obviously this phenomenon isn't limited to fanfiction or even writing, but it seems to me that there are (at least) two styles to long writing projects:

1. Serial: Pushing through to the end on a long-fic before starting a new one, or
2. Parallel: Writing multiple long-fics side by side, depending on what feels right to write at any time.

I'm curious where other writers see themselves in this split, or if they do at all - maybe I'm totally off the mark!

As far as I go, I definitely fall into the first bucket, even when it's tough & I reeeaaaalllly want to explore the new shiny idea my brain has come up with. There's a sense of completion that comes from focusing on one core project & knowing that I'll see it through to the end. Sometimes my brain won't let me write it for short periods & I'll jump away from my long-fic to write a one-shot or shorter multi-chapter story but I don't maintain multiple long-fics at the same time because I'd just get confused & struggle to relate to my story (especially as I focus on the same characters/fandom for all my writing so far).

I'm always hugely impressed with writers who manage to juggle multiple long-fics at the same time, even if they don't finish some of them. It seems to me like it'd be a lot less stressful to be able to just write whatever inspires joy in the moment & leave a story without the need to complete it - I'm totally aware this is a "faraway fields are greener" situation, but it's nice to think that it's a more enjoyable approach.

I recently came across a writer who's maintaining at least 3 long-fics that I could see & every new chapter comes with a note at the end saying which story is next on the list to be updated. Now, chances are they have at least one of these fics pre-written, but either way, I'm in awe of them. 😮