The rapid proliferation of cryptocurrencies such as Bitcoin has brought world’s attention to a fascinating idea by economist Friedrich von Hayek: competing private currencies. In the Nobel laureate’s 1976 book, Denationalization of Money, Hayek argues that there is no innate reason for governments to have a monopoly on money. He advocates a system of private currencies in which financial institutions and individuals create currencies that compete for acceptance. Hayek also points out that stability in value is presumed to be the decisive factor for acceptance. Cryptocurrencies, thanks to their innovative solutions to decentralization and privacy, have become popular contenders in the private currency competition. However, major cryptocurrencies are subject to massive price volatility, making them attractive to speculators but unsuitable for mainstream use. Inspired by the trilemma in international economics, we hereby propose the impossible trinity of cryptocurrencies: a blockchain economy cannot achieve all three of below goals at the same time. In pursuing any two of these goals, the community must forgo the third. a) A deterministic currency supply b) hypergrowth in ecosystem activities c) price-stability of the underlying currency Majority of blockchain economies have been experiencing the same scenario: a deterministic currency supply and hypergrowth in users & transactions. This setting results in high volatility of underlying currency price, which in turn magnifies the currency’s speculation, undermines its potential as a medium of payment, and hinders its real-life adoption. Take Ethereum, the leading smart contract platform, for example. The built-in currency ether (ETH) is playing a dual role with conflicting purposes: As the network fuel and medium of exchange, ether is expected to be spent whenever users need services, which requires shortterm value stability. As a digital asset, ether is held for long-term appreciation and traded for speculations. It would be a good idea to segregate ether’s dual role to better serve respective users for different purposes. Instead of creating new credits by collateralizing external assets, we propose an innovative contract that will retain ether’s value but transfer volatility from risk avoiders to risk seekers.