my pet theory on the "nuclear fusion is coming in the next 20 years" thing is that science journalism has reported on every minor breakthrough related to fusion technology. being able to theoretically confirm it, being able to actually accomplish a test run, being able to use some other forms of nuclear fusion (like a tokamak vs a stellarator), being able to very recently, break even. Earlier on, in the optimistic post-war nuclear period, some dipshit probably gave an estimate that we'd have it in the next 20 years because everyone was so optimistic, and ten it stuck around. so every time someone brings up nuclear fusion, which happens a decent amount, the "it's only been 20 years away for the last 80 years" remark gets popped off and spreads around without any really clear origin point. I think probably also the sheer number of breakthroughs reported over time means that people are going to be skeptical, since everyone interprets science journalism as always reporting on the one life-changing breakthrough, rather than just being a kind of steady background noise, like any journalism.