A friend of mine sometimes refers to writing as "going into the word mines", which is a very nice metaphor, if I do say so myself. Not only because it conjures up the image of hard, grueling work to bring up a few precious gems, though that is a key reason.
Part of why it works for me is the image of the mine itself: filled with large passages and twisty tunnels. I like to think, when I'm working on a specific project, like I'm supposed to be right now, I'm going down that specific tunnel. So, right now, the Holver Alley Crew tunnel is the one I'm supposed to be working on. I've gotten almost all the words out of there, and then it's just a matter of putting and polishing and putting them to market. (Go with me on this metaphor, will you?)
However, when I go down into the mines, I make some discoveries. I've found a whole new vein of words in the Maradaine Constabulary tunnel, so once I've finished in Holver Alley, I'll have plenty to do there.
(And there are, of course, the tunnels that dead end, that turned out to have no words to mine. We won't get into that.)
But then there are the times when you find a whole new tunnel. One that might have thick, rich veins of many shiny, sparkly words.
The ground shifted on me while heading down to Holver Alley, and I saw a shaft leading to a whole new tunnel. I peered down, as you do. I wasn't ready to go down and start working, of course, but I wanted to know what might be there.
I saw a ship, and a crew. A crew of rough-but-decent-hearted privateer types. On some level, the crew and the ship were completely clear to me. I knew exactly who they were and what sort of adventures they could have. In my Space Opera timeline they could fit right in, cruising around the asteroid belt and the outer planets on a solar-sail ship in the early 22nd century.
Then I looked again, from a slightly different angle. The same basic crew, a very similar ship, but... not quite. Suddenly they were a Steampunk crew, cruising around the uncharted west of North America on a sailed-airship in an alternate 19th century.
And I felt a bit of panic. I really could go either way with them. Except I don't have a Steampunk setting that I've done the worldbuilding for. Not yet, anyway. But this crew might inspire the idea that I need to.
So, that's the thing to figure out: are they Space Opera, or are they Steampunk? Not sure yet.
In the meantime, I've got to go into the mine to finish the Holver Alley re-write.