[Xixi]

It's trust: if people in general stop trusting Bitcoin its value will very rapidely converge to nil. Because there's nothing to back up its value, it will stay there and never recover, and will be remembered as the 21st century tulip bulb.

On the other hand take gold: as a metal, it has little practical use (compared to its availability, it's not that scarce), yet its value is still up there after several thousand years of use. Why? Because there's a consensus that it's worth something, and trust that this value will remain (and even go up) in case of war/disaster/etc. Bitcoin could be a new gold. That's highly hypothetical.

Don't invest what you cannot afford to lose.