When you're a writer, the question people always ask you is, "Where do you get your ideas?" Writers hate this question. It's like asking Humphrey Bogart in The African Queen, "Where do you get your leeches?" You don't get ideas. Ideas get you.
You see something or hear something or read something, and unlike the hundreds of other things you've seen and heard and read, this one triggers something--some connection nobody else sees--and you know you'll never be able to explain it. So you write a story about it.
"Idea" is even the wrong word. it implies something rational, a concept, a thought, and there's usually nothing rational about it. It's not a light bulb going on over your head. It's a tightening of the throat, a shiver down the middle of the back, a stab to the chest. Or the sudden impulse to shout, "Get out! Before it's too late! Run!"
Reading it made me sort of bubble up and start giggling to myself, because, well, THAT'S IT! I've never seen it described better than that. That's it, exactly.