For something to be a major milestone towards opening up new opportunities, there is a need for various influential people and powerful people to say that it's not possible. If a large group of influential and powerful people already agree that something will probably work, then it's probably just an incremental improvement, and one of those influential people would have already made it happen, or be working on it.
Breakthroughs are usually first seen as fallacies and follies. If they are not initially seen that way, it's probably not a breakthrough.
I'm not saying that all fallacies and follies are breakthroughs, but it's a necessary phase for it to be considered that way. All breakthroughs were first broadly considered to be fallacies and follies at one time.
People can't fly, they aren't meant to, flying is for the birds. Starting a car company in the 20th century, and having it make electric cars is doomed from the start. A rocket company startup is doomed when it's trying to make rockets that come back and land vertically, and will never lift payloads cheaper and more reliably than the incumbents. All those things had been broadly considered proven to be bad ideas that will fail. People tend to have short memories and have forgotten how negatively those ideas were perceived originally.
Yet, they happened and changed everything.