Democratic politics makes savvy people stupid, at least when they act politically. This has long been demonstrated, and it applies both to voters and policymakers. Several things account for it: the impotence of one vote, the consequent futility and hence wastefulness of acquiring information, the dispersal of the costs of government, and the resulting theatrical mood-setting farces called election campaigns. Outside politics life is rather different. Our actions have a reasonable chance of making a difference to ourselves and those we care about; the costs of our actions fall largely on...