https://en.wikipedia.org/wiki/Technology_readiness_level
There are entire closets full of ideas that are conceived, modeled, simulated, and reports that end with "this will probably work except X doesn't exist yet." A lot of the time X is a material, but it might be a bandwidth issue waiting on a modulation technique, or a more precise widget, or a social problem where the technique is valid but the side effects aren't "palatable".
NASA couldn't afford to risk the kind of failures SpaceX saw early on because of how it would affect their overall funding. SpaceX captured lots of high def video and telemetry and powered through the failures. I wish I knew what technology the world was waiting on, but since China has the vertical rocket reuse now and Japan is working on it we really are living in the future where it's commonplace.