Short-term collateralized debt, private money, is efficient if agents are willing to lend without producing costly information about the collateral backing the debt. When the economy relies on such informationally-insensitive debt, firms with low quality collateral can borrow, generating a credit boom and an increase in output. Financial fragility builds up over time as information about counterparties decays. A crisis occurs when a small shock causes agents to suddenly have incentives to produce information, leading to a decline in output. A social planner would produce more information than private agents, but would not always want to eliminate fragility.