Well, that's both difficult and easy to answer. Ideas don't "come" from anywhere; they simply exist. At the same time, they're built from everything. Every sight, sound, smell, memory and experience filtered through your unique personality and perspective is an idea. A minute detail that 761 people have overlooked may fire off a creativity explosion in your head.
One of the hardest things for non-writers to understand is that YOU CANNOT TURN IT OFF. Ideas keep coming. They form unions and picket your brain. They fight turf wars over your attention. They butt in on each other when it’s not their turn to be written.Your mind is the primordial soup of the universes of your own creation, and it's just waiting for you to drop a line and catch something.
A writer will come to a point of choice and pick a direction, but the possibility of that other choice will spawn an entirely new idea. Then your tenth grade English teacher’s voice pops into your head, reciting “The Road Less Traveled” and suddenly that other idea now stars a guy named Frost because there’s no other possible name for him. (Fanfiction thrives on this sort of thing.)
Schrodinger and his cyanide-huffing cat had nothing on the infinite possibilities that live inside a writer’s mind. To a writer, there’s no question that multiple universes exist because we see them all, simultaneously, running side-by-side with their infinite branches splitting each possible storyline.
And it NEVER STOPS.Which brings me, finally, to this:
I have finally tracked down the definitive answer to "Where did this idea come from?" concerning Arclight. I went data mining through all the junk I've saved from way back when and found it. So are you ready for the reveal? Ready? Ready?
The answer is... ANTS!
Not the creepy CGI version with a "z" at the end, but actual ants. Army ants to be precise. That which became Arclight came from a nugget of an idea after learning about a troop of army ants that swept through a village in South America. There was a description of a person glancing at their wall, at night, and saying that it appeared the wall was moving. Then they realized it was ant season, freaked out and ran away because the swarm was unstoppable.
So there you go.
Tolkein watched a Shakespearean play as a boy, and in his disappointment that the "moving trees" were nothing but an army with heavy horse, he created the Ents.
I see a story about army ants, and in my disappointment that the "moving walls" were nothing but said creepy crawlies, I created "The Fade"