Jonathan Gruber, teaching MIT's 14.41 Public Finance and Public Policy, lays out the economic logic behind social insurance programs like unemployment insurance, disability insurance, and workers' compensation. He explains why private markets fail to provide adequate insurance against income loss, covering adverse selection and moral hazard as the twin problems any public program must balance. The lecture works through the tradeoff between consumption smoothing, which argues for generous benefits, and the incentive costs of insurance, which argues for limits. Gruber connects the theory to inequality and government transfer programs, using models and examples to show how policymakers weigh the welfare gains from protecting people against risk against the efficiency losses from reduced work incentives. Runtime is 78 minutes, delivered as a standard lecture-hall session with blackboard-style economic reasoning throughout.