What causes the tulip bubble to burst was actually the black plague coming to town. Sure, the prices was blown way out of proportion, but everyone was in this rational bubble until they didn't dare to go outside to join auctions. The sellers still had to go as they had mortgaged their houses and whatnot, and this caused the markets to realize that it was buyers market. Buyers market in a situation where there is a very small intrinsic value might cause a crack, like it did. Let's hope it's not the case for crypto also.