Determine Scope Of The Game

I know the game I would like to write about, but what game should I write?

In his Podcast The False Dawn of the Electric Car, author Tim Harford references the concept of Adjacent Possible as described in the book Where Good Ideas Come From: The Natural History of Innovation. by Steven Johnson

A distillation of a concept is that a transition is easier when taken in smaller steps.

So taking stock of my gaming knowledge at this point, I ponder on its logical progression to the game I would like to write.

• I think of it as a journey with several rest points (milestones).
• I deliberate the first stop and see what skills need incremental development, and what new skills may be needed.
• I check the Unity modules concerning “Project Design Documentation”.

Yep, seems like I will be writing the game before the game, before the game.