It Cuts Both Ways
Sometimes your inspiration starts with the Big Idea, or maybe the starting point is a particular character, or a name for a character, or a plot twist. No matter how your inspiration usually arrives, the project will ultimately rely on having all the pieces fit together.
All of that is basic, intro-to-creative-writing type stuff, and none of it is specific to collaborative writing. However, the experience of getting from the initial flash to the actual writing is a lot different for partners. It’s kind of a double-edged sword.
You have to find subject matter that both partners are interested in. No matter how well aligned your tastes and styles, it’s likely that you or your partner will occasionally feel inspired about something that the other simply doesn’t care for. The idea might be fantastic, but still not turn out to be something you can collaborate on.
On the other hand, there could be other reasons that you struggle to win over your partner to your idea. Maybe it’s not as shiny as you think it is, or maybe it’s just not quite ready yet. Working on your own, you would probably chase after your exciting Big Idea, wanting to pounce while you feel inspired. You’d only discover its problems after devoting a lot of time and effort to a draft.
In our case, an idea can fall down at the conceptual stage mainly due to not being quite the right kind of science fiction. There’s a certain type of world-building that we do well together. Our story worlds generally only diverge from consensus reality at a submerged level. They look superficially like the real world, but harbor deep and sinister differences. So, for example, a far-future setting represents a major stylistic and procedural shift for the writing — different kinds of research, different pacing for exposition, different priorities. Meaning there will be an uphill journey for a Big Idea that needs a far-future world in which to thrive, and if we come up with a different inspiration we’ll probably follow it instead.
Not that it’s impossible for us to imagine working together on different types of fiction, just that it’s not healthy for the partnership to try to force things.