There is no underlying value to Bitcoin and many other cyber currencies. If I own gold, Nvidia stock or a U.S. Treasury Note, there is an underlying asset that will always have value. The value of Bitcoin is determined by the Greater Fool Theory. In this case, the theory says that the value of Bitcoin will only rise if there is someone more foolish than you are buying it.
I saw this in the '80s with farmland in Illinois. The only way farmland was a good investment then was if the value continued to increase. Eventually, the bubble burst and many people lost a lot of money. Bitcoin is no different. Anyone who bought Bitcoin at $19,000 each realizes that.
When I posted this on LinkedIn, someone asked, "But what about cash, specifically, United States dollars?" This isn't about cash, this is about investments. If you consider Bitcoin an alternative investment, then why are you calling it a currency?