Some of the great explorations of history, such as those of Speake and Burton, were determining the sources of the Nile. Was it a spring bubbling in the Mountains of the Moon, perhaps it flowed from Lake Victoria in Kenya. or even in some hidden glen deep in the Nyungwe Forest in Rwanda? Eventually it was determined that there was no single, definitive source, but that the Nile was the result of outpourings from smaller waterways spread over one and a quarter million miles or more of collection basin throughout central Africa.
I often wonder where my own ideas came from when I complete a story, or sometimes, even a single scene or passage. Was it spurred by something I'd read in my earlier years, an event in my life, something mentioned in a casual conversation, or even something once read and then forgotten, only to emerge years later clothed in different expression? There are a few stories that I can point to and say "Yes, this is where I got the idea," but truthfully that might only address the macguffin, the punch line, the setting, or the character's makeup, not all the other stuff that fills the pages - all the little ornamentation, snippets of conversation, and observations that well up unbidden and pour onto the page without my conscious control.
In the end I ask myself where does the Muse, who inhabits me when I get into the fugue writing state, find these things, all these niggling details, all this color and sound and smell and action? How does it happen?
An example: In my story "Primrose & Thorn" the Jupiter sailboat and its environment came from careful research and the story's plot was carefully contrived in advance, but nowhere in my mind had the characters of Louella, the lusty, direct, and black female protagonist and Pascal, her french companion been formed. As I was writing my Muse gave Louella birth and let her rise entire, like the Botticelli Venus, from the sea of unconsciousness and step into the story. For certain her character and behavior grew out of the necessities of the story, obstensably a vehicle used to put my feelings about sailing in a way the reader would enjoy, but she had her own personality formed from the type of challenges she'd faced. I am certain that I've never known anyone like either Louella or Pascal, nor are they amalgamations of people I've met. So where did they come from?
Perhaps, like the sources of the Nile, the content of my writing drains from the broad timescape of a lifetime of reading, experiencing, and discovering my world. Perhaps it is something best not explored to discover the source, but only to marvel that it is there for the Muse to use.