We model a cryptocurrency as both a membership in a decentralized digital platform developed to facilitate transactions between users of certain goods or services, and as an investable asset for speculators to capitalize on the growth of the platform. The rigidity induced by the cryptocurrency price having to clear these two sides, especially with strong complementarity in membership demand, can lead to market breakdown (no equilibrium). While user optimism mitigates the market fragility by increasing user participation, speculator sentiment exacerbates it by crowding users out. Informational frictions attenuate the risk of breakdown by dampening price volatility and average platform performance. Furthermore, while strategic attacks by miners do not directly lead the platform to break down, the users’ anticipation of losses from future attacks exacerbates the market fragility.