You can break down the world into the 99% that "know" that it's impossible. They'll never invent that world-changing thing.
That leaves 1% that "don't know" that it's impossible. Of that 1%, 99% will try and fail.
The remaining 1% of the 1% succeed, like George Dantzig (who came late to a Stats class at UC Berkeley, thought some problems on the board were homework, and a few days later handed the professor solutions to some famous open problems in statistics), and Jack Kilby (who, seeing computer performance limited by the number of wires soldered by hand, demonstrated -- against the protests of his "we-know-better" co-workers -- that you could get rid of the wires, resulting in the integrated circuit).
It's important to remember the 99% of the 1%. There are probably people on HN who have tried and failed. But rather than simply saying that it is impossible, we should encourage people to share share how and why the problem is difficult, so that hopefully the next person to try won't waste their time retracing the failures of the previous generation.