An example: Two days ago, I was in the bathroom of my hotel room, reaching for the vitamins I take every morning. They're brown pills, and I carry them in a plastic bag. Just as I reached for them, one of the "pills" moved.
In point of fact, the pill was some kind of roach. It was the size and shape of my vitamin pills. Perhaps it saw the vitamins, and thought its fellow roaches hadn't invited it to the party. So it went in the bag with them.
When I touched the bag, the roach scurried out. And naturally, I turned into a screaming roach destruction machine, karate chopping everything in the bathroom trying to kill the damned bug: "Crush, kill, destroy!" I finally got the damned thing. I'm just amazed I didn't destroy the bathroom.
Then, I took my vitamin. I decided I wasn't going to let the fact that a roach had been snuggling up next to the vitamins stop me from taking one. But as I swallowed it, my writer's brain kicked in. A scenario unfolded in which I reached in the bag, grabbed a "vitamin" and put it in my mouth, only to have the vitamin/roach suddenly sprout legs and run down my throat. Of course, I would have probably collapsed right then. And that's how they would have found me, sprawled on the floor.
And that basically describes what it's like to have a writer's brain. All sorts of scenarios play out.
Another one: I'm staying at the Best Western Southbay today. It's an interesting hotel, with a strange vibe. Breakfast is served at an adjoining restaurant. The Restaurant is a Chinese restaurant -- so Chinese that even the menus are in Chinese (they also have pictures).
If you can see the freestanding menu inside the doorway, it's in Chinese.
All but one other patron was Chinese. It was packed. So I'm lucky they found me a little table in the corner, more of a service tray than a table, next to the other non-Chinese patron. He seemed hispanic.
Anyway the first thing that I heard him say was "so is that the gravity you grew up with?" Immediately that sent my writer's brain into overdrive.
As I eavesdropped on his conversation, it became obvious that he was saying "grandmother" in an accent. But it was too late. My writer's brain had spun out a scenario where aliens concealed a base on Earth by hiding it in a Best Western (because of course!). But Earth culture is one big blur to them, so they didn't realize a strongly ethnic Chinese restaurant would be out of place next to a Best Western near the Los Angeles airport.
And the customers were aliens, but disguised as Chinese, of course, because there are more Chinese than any other ethnicity, and the aliens are trying to blend in. In fact, the lobby of the Best Western that morning was packed with Chinese people.
Or were they?