I’ve been convinced, reluctantly, for some time by an argument regarding inter-stellar travel. The possible means we might have for traveling between the stars within reasonable time frames imply a command of massive energies. Wormholes, warp-drives, and hyperspace all imply direct manipulation of space-time in a way that we can observe does not currently occur routinely. Necessarily, such technology (if it were possible) would require scientific know-how we do not have but also massive energy.
The sad conclusion of this argument is that interstellar travel can never be the basis of a galactic civilisation of the kind we see in our space operas. Having gained the necessary pre-requisites of large-scale energy manipulation, humanity would have no need for interstellar trade or indeed much need for interstellar exploration for reasons other than pure curiosity. Put another way: faster-than-light travel implies a post-scarcity civilisation and almost god-like technology.
I’m a tiny bit more sceptical of that chain of thought now though.
I think it is partly shaped by our current perspective on energy. It is easy to see energy as the core limitation of our economy. You need the energy to do anything. To enact any kind of change, to hold off entropy, to shape things requires energy. Simply to stay alive and warm and fed requires energy. Our view of energy in modern society is one that sees energy as a limited resource that is inherently expensive. However, that is misleading.
In space and in the universe in general, massive sources of energy are plentiful. Simply looking up on a cloudless night will show you a practically uncountable number of active fusion reactions boiling off photons into space. Energy itself is plentiful, what is rare or difficult to acquire is energy that is usefully constrained at a scale that is useful for human purposes.
The canon was invented before the steam train. The fusion bomb was perfected before the fusion reactor. Deploying huge amounts of energy is not necessarily technically difficult, what is difficult is deploying huge amounts of energy without wrecking stuff. Of course, that doesn’t mean making wormholes in space to travel to distant planets is feasible but it does make me think it might not require a level of finesse over physics that could be applied to more subtle things.