«Ludwig von Mises showed that money prices are not arbitrary; it really means something when a firm suffers a loss. Specifically, when a firm loses money it means that customers are not willing to pay as much for the finished product (or service) as the firm had to spend acquiring inputs. Loosely speaking, then, a firm that loses money is one that takes valuable resources and turns them into something that society values less.
Mises put his finger on the fundamental problem with socialism. If the state owns all the resources, then there can be no market prices for the tractors, kilowatt-hours, barrels of oil, and other things necessary for production. Looking at the various productive enterprises in operation at any moment, the central planners won't have a common denominator for all of the different combinations of inputs going into each one. The planners won't know if a particular car factory "makes sense," because they will just have an enormous stream of data describing the various resources going into the factory, and the amount of finished cars coming out of the factory. These brute facts alone don't tell the planners if they are efficiently using the resources being consumed in the factory.»