The answer would then be: it came from Schenectady.
I think that's a great answer.
I also think there are some fun stories there...
To be precise, from a mail order firm in Schenectady. From which you can order five, ten, or a bargain twenty-five ideas a month.
I've heard of a writer driving near Schenectady and wondering whether she should look up their outlet, for the slightly blemished ideas. . . .
I tend to find ideas lying around in the street. Literally.
Yeah, one day I saw a glove lying in the road and thought "Huh. You see single gloves and shoes abandoned, all the time. Hey, what if the hands and feet were still in them?"
I hate my brain.
Another story was spawned by an abandoned downtown street in St. Louis and some of the fabulous architecture there. I wondered why all the stores were closed and no one lived there anymore, and came up with a scenario.
Some ideas come from random trains of thought. Some from the news. Some from reading/watching/playing something and going, that's interesting, but I would have done it differently.... Which I use to feel bad about, until I saw Gene Wolfe answer this question in an interview. His answer? "Well, that's interesting, but I would have done it differently."
Some from the news.
Oh yeah! It's so much fun to read the newspaper and fill in all the details they leave out! I remember a story years ago, about a small Buddhist monastery out west in which half a dozen monks had been found murdered. It ended up being a gang-related incident, but in my imagination the monks died when the unholy Cthonian monster they were guarding got loose. *hee*
Then there's always steal the idea from another work of art and file the serial numbers off.
Best to do it with backstory or when you think they wasted, wasted, wasted that really nifty idea.
My favourite thing is when I come up with a relatively weird or crazy idea and people ask me what drugs I was using when I thought of it. Because obviously creative thinking doesn't extend to bizarre concepts like harvesting lake spiders for curative properties, so I must've been pounding the amphetamines, right? _-_
I've taken to telling these folks that I'm sorry their brain isn't coming up with any new thoughts, because that means they're clinically dead. Then I write "HI, I'M A ZOMBIE!" on a post-it and stick it to them. (Actually I only did that once, but it went down pretty well so I'm probably gonna keep doin' it.)