Sometimes it's surprising what nobody was interested in inventing. I think Grace Hopper is really important because people were resistant to the idea that programming the computer involved boring mindless steps which could be done by a machine and so of course instead of hand writing the program in machine code you should write a higher level language and have the machine translate that. It's incredible now, but this very idea was once an important invention and yet her superiors were not enthusiastic.
Bernhard J. Stein's *Resistances to the Adoption of Technological Innovations" (1937) is a fascinating read in this regard:
https://archive.org/details/technologicaltre1937unitrich/pag...
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I'd heard of it via Isaac Asimov who mentions it in his biography and a few other contexts. Asimov was Stern's research assistant, and incorporated the ideas into several of his own stories.
Your transoceanic cable example is an interesting one, as the first electrical / telegraph cables greatly expanded the understanding of electric fields and interactions with the environment, especially in salt-water.
I'm also wondering if there's some sort of frontier between the "just blundering around" approach --- mass parallel experimentation --- and "requires a substantive theoretical understanding". To take your LED example, LEDs are the inverse of the photoelectric effect (and apparent PV panels will emit photons when a charge is applied to them). Electroluminescence dates to 1907, whilst the first LEDs were developed in the 1960s. There were earlier similar phenomena such as chemoluminescence (including numerous examples of bioluminescence) which might have suggested the possibility.
I'm agreeing in part, disagreeing in part, and wondering if there might be a more robust or systematic way of distinguishing limits of both methods.