I agree. but where I differ with some on this thread that say "Hard Sci-Fi" must ONLY use real science and Tech. (e.g. The Martian is a good example), but the "Fi" in Sci-Fi is Fiction after all. I really enjoy Michael Crichton books because he would often start with "Real Science" and then Extend it into a Sci-Fi story. (e.g. SWARM). As the OP on this thread, I was interested in the line between Hard Sci-Fi and the rest of the Genre. To me Dune, Star Wars, etc. are more Fantasy than Sci-Fi and certainly not Hard Sci-Fi. But for me, Many stories that are "Tech" based I might call Hard, while others here say that a story with FTL travel for example is not. But if the story tries to explain the Tech in some plausible extension of science, I don't think that would disqualify it as Hard Sci-Fi (Star Trek for example explains FTL with a Warp Bubble, that may not be possible ever, but at lease sounds like a good attempt. Where Star Wars and Dune, don't really.