VTVL (vertical takeoff, vertical landing) rockets have been talked about since sci-fi in the 30s and seriously since the 50s. We only just started getting real ones (SpaceX, Blue Origin), though in the 90s there was a prototype called the DC-X that proved the concept at a smaller scale. You can find DC-X videos on YouTube.
The fact that something was talked about long ago and we don't have it yet doesn't necessarily mean there's something wrong with the idea. Sometimes all it takes is for someone to just do the engineering, which with high-capital stuff means it also takes someone being willing to pay for it.
Of course the other case is things like net-positive fusion where people have been doing the engineering but it's f'ing hard. Still given the progress that has been made on fusion I get the sense we could do it if we spent more and put more parallel effort into it.
The fact that something was talked about long ago and we don't have it yet doesn't necessarily mean there's something wrong with the idea. Sometimes all it takes is for someone to just do the engineering, which with high-capital stuff means it also takes someone being willing to pay for it.
Of course the other case is things like net-positive fusion where people have been doing the engineering but it's f'ing hard. Still given the progress that has been made on fusion I get the sense we could do it if we spent more and put more parallel effort into it.