Concorde was also a victim of something else getting built that people went to instead— widebody business class. It turns out that a lie-flat business bed for seven hours is more appealing to most people than a cramped, economy-style cabin for three and half hours.

Solar Roadways was also obviously going to be several orders of magnitude more expensive than traditional asphalt, even with very generous estimates in in Solar Roadways's favor, but people still dumped a few million into that scam. And several governments (i.e. France) even wasted money on larger implementations of it despite failing even the most optimistic back of the envelope calculations.