Fiat currencies (dollars, euros, yen, etc.) have an unlimited supply – central banks can issue as many as they want, and can attempt to manipulate a currency's value relative to others. Holders of the currency (and especially citizens with little alternative) bear the cost.

With bitcoin, on the other hand, the supply is tightly controlled by the underlying algorithm. A small number of new bitcoins trickle out every hour, and will continue to do so at a diminishing rate until a maximum of 21 million has been reached. This makes bitcoin more attractive as an asset – in theory, if demand grows and the supply remains the same, the value will increase