But why bother with cost-benefit analysis at all? What is wrong with deciding whether or not to undertake any specific investment, or to choose among a number of specific investment opportunities, guided simply by proper accounting practices and, therefore, guided ultimately by reference to profitability. The answer is provided by the familiar thesis that what counts as a benefit or a loss to one part of the economy - to one or more persons or groups - does not necessarily count as a benefit or loss to the economy as a whole. And in cost-benefit analysis we are concerned with the economy as a whole, with the welfare of a defined society, and not any smaller part of it.