Most informal finance comes from family and friends. Existing informal finance theories cannot match two characteristics of family finance: family investors may accept below-market or even negative returns, yet borrowers often prefer formal finance. We argue that social preferences make family finance cheap but create shadow costs that nonetheless discourage its use: Committing family funds to risky investment displaces intrafamily insurance and undermines limited liability. The same characteristics that sustain familial insurance thus render family finance a poor source of risk capital. Even when overcoming capital constraints requires social ties, intermediation and semi-formalization may therefore be crucial for promoting risk taking.