It's a process where, like, if I were to snapshot where I am today, I've got 10 different story ideas that are circling my mind today, that are contenders for what I could write next. I'm in the process of writing something else, but those stories are there in my head too.

They're all in different stages of development. Off the top of my head...

1. Anthology series that I enjoy enough to have written a dozen chapters for, but I have to wait before starting it (lest I put too many books in the same setting in a row and fatigue my audience).
   
2. Story that I like the idea of, that just needs a piece to make it 'click'.
   
3. Another story I like the idea of that I may need to just sit and write out before it clicks- different sort of click required.
   
4. And another that's just an interesting musing that I haven't really developed, test written, or anything, breaking away from my tendency to do magic and superpowers: a crime drama, just to explore character work and step away from what may be crutches I lean on.

And in reality, each of those things has about a dozen loose ends - the anthology story has 3-4 plots or ideas I like for sub-stories that haven't clicked or that need good characters. The 2nd story has a few things I just don't know how to tackle, including the ending which is momentous and intense and puts a question to the characters... and I have no idea how they'll answer. The 4th is totally open-ended.

And in the course of writing the chapter I'm working on, I could think of a gritty, tough character who is more aggressive, defensive, and reactive than others I've written before... not a fit for the chapter or the scene I want to do, but in a quick check, I might cross-check with bullet point 1 above, rolling it against some of the unfinished anthology ideas (does this character work for this idea? No? What about this one? No. What if I took this one anthology story with a total sweetheart at its core and dropped a tough abused kid into it instead? Doesn't work at all, but that spurs on this idea...)

And it could be the low-to-the-ground character perspective that lets me figure out an angle to answer the tricky ending in story 2, or make it 'click'. Or a side character dropped into 4- which is something that works more the more I can think about it.

Or it could be that I stop and contemplate just why I haven't written this kind of character more, or what I like about the conceit, and apply it to story 3, to see if it sparks something- even by me feeling compelled to do the total opposite.

Sometimes that's a whole tangent from my current work, but oftentimes it's a flash in the pan style thing, a quick rundown, compare and contrast through stuff I've got in my head. And it's not always a story element- it could be me noticing particular weather, or dwelling on particular childhood memories.

It's not 'Story A, start, get it finished, polish... come up with story B, start it, get it finished, polish...' - it's a jumble, overlapping, so everything's in some state of development all the time.