The real value of a currency lies in the fact that it is a medium of exchange. Any currency is only useful if enough people agree to use it. So whenever you invest your value in money (yes, even and especially govenment paper money), you take a risk that your value could shrink or in extreme cases vanish, because you are not entitled to other people trading with you, if they don't value your medium of exchange. Even gold wouldn't be nearly as valuable if it was just a commodity for use. The point bitcoin advocates make is that bitcoin COULD potentially be a much better currency IF enough people were to use it, because it can't easily be inflated, stolen or taxed (but I repeat myself), and it can be transfered digitally while being anonymous and without much efford. If you decide to invest in bitcoin, you hope that enough people in the future will be using bitcoin for it to have value, just like you do when you use gold or silver, or dollars (which are constantly de-valued by central banks). The alternative to using a currency is substisence farming or bantering for goods and services.