First it was tulips. More recently it was tech stocks and then the housing market. Lately, its all about bitcoin.
All four share a common denominator: They suffered through financial bubbles, or bubble-like conditions. The first three ended badly. The jury is still out on whats in store for bitcoin.
The unfortunate thing that may happen to bitcoin is that it is not really supported by something physical and for that reason could be a way bigger bubble. Houses, stocks etc all generate revenue in some way themselves so have some level of inherent value whereas simply owning bitcoin does not make you money other than via price increases.