It can take a long time though, and while you're riding the upwards curve and selling slowly you can make a lot of money. The thing that people always forget when they read about the tulip bubble and he wall street crash is that as many people became rich as went bankrupt. It's a zero-sum game, so every dollar someone loses will be won by someone else. In many ways, it resembles a poker game where both players are bluffing. Eventually either one will fold or they'll call and whoever has the higher card will win.
I have not speculated on bitcoin, because I don't have any confidence that I can predict the inflection point well enough to find a greater fool before it does.