Should you finish one project before you start writing another?
I've known several writers over the years who were great at starting projects ... but who never seemed to finish anything.
(If you're a fanfiction reader, you'll probably also know the frustration of waiting for an author to update a work they started literally years ago, while watching them publish new works in entirely different fandoms...)
I get it, though. I spent years of my writing life not finishing things. New projects felt exciting, but
often my energy petered out a few chapters into a novel, or I'd start on a short story idea only to find that I didn't want to complete it within just a few thousand words.
There's nothing wrong with false starts. You don't have to finish everything you start writing, just like you don't have to finish everything you start reading. A project might feel promising at first, only for you to
hit a serious roadblock partway into it.
But if you find yourself doing a bit more starting than finishing, you might want to commit to finishing at least one of your on-the-go projects before starting a new one.
(It can also help to deliberately abandon a project, rather than just
set it aside: then at least it's not still tugging at your attention.)
Sometimes, though, working on two projects at once can help you get more momentum, not less. Perhaps you're feeling stalled or stuck on your novel ... but taking a break to write a short story could refresh your creative energy. Or maybe you want to start jotting down some ideas for your next novel while you're editing
the current one.
There's no "rule" about how many projects you can (or can't!) have on the go simultaneously. What's important is that you're enjoying writing. That could mean sprinting to the finish line with one project ... or it might involve taking your time and switching between several different projects, as the mood takes you.