In this case though, nobody was using it to mean "hard". There really were PhD Physicists arguing at length that it was physically impossible to do this.

That's why it's an interesting story.

No one ever argued that it was impossible to use wind energy to move faster than the wind. The real problem here was describing the effect as sailing directly downwind. The "sails" (on the prop) do not go directly downwind, and there's stuff going on that isn't best described as "sailing". But by describing it that way, people managed to extract blustery pronouncements and explanations of why it was impossible (which sailing downwind faster than the wind is).

You can prove impossibility. It's easy to see that you cannot sort any arbitrary sequence of N arbitrary items in less than N elementary operations, for instance.

That said, yes, it's use as a shorthand is misleading and annoying.

Colloquially, "impossible" = "I don't know how to do it", "trivial" = "I know how to do it". These two terms have very little relation to whether something is actually impossible or trivial, but are a pretty useful shorthand for "Get someone else to do this" vs. "I can do this". Most good managers understand this, and will push you to do impossible things anyway while padding your estimates for trivial things by a factor of 10 or so.

A corollary is that if you want to expand your skills, work on impossible problems. A second corollary is that more entrepreneurs should be working on impossible problems, because the small number that are actually impossible is outweighed by the heavy returns for the ones that aren't impossible but scare off competitors because they look that way.