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Just a random, fun question I was kind of curious about; sorry if I tagged it incorrectly.

I'm wondering if there are any famous StackExchange or Overflow posts (math, physics, comp sci etc) where someone sort of naively makes an interesting observation which later developed into a (relatively) big deal? I kind of imagine these sites have been around for long enough that maybe some big idea or construction originated from someone just riffing on a question, comment or answer.

In addition, I know there are tons of posts with someone seemingly naively conjecturing a proof to an open problem, or a new proof of something known. Any famous examples of this which turned out to be correct and important?

citation needed$\endgroup$ – Yemon Choi Jul 3 '17 at 4:04