That was the crass money-making part of it, but a lot of nerds earnestly believe(d) that cryptocurrencies would have massive world-changing consequences. I think it's increasingly obvious that there's little rational or empirical basis for such belief.

With AI, the biggest claims I see are overwhelmingly from people who are not doing cutting-edge work in the field, who have no real foundation for a belief that these AIs will continue to improve at a dramatic rate. Because to really change the world, they do need to get a lot better.