Speculative fiction is based on what if. All it takes is one small question to begin the process. What if?
It’s after that – the process of building the then what‘s that really builds the world from the writer’s mind. The then what‘s nail down the particulars. After that, a story shines through.
But don’t think I’m advocating a story about a thing- stories are about people. The character must change; that is the beauty of story.
Ransom Noble 
The “what if” is the key to writing anything. Good point.
I like to use the “what if” to develop stories. It also is of good use for a prompt based contest, like the one I have on WDC. I give the what if and the author handles the then what.
Good topic for the blog. What if… 😀