An example of the Economic Calculation Problem goes as follows: How would railroads be built? If we were to take out the mechanisms of a market provided by Capitalism & replace them instead with what the marxists want, this problem would be unsolvable. In a marxist economy, prices & any form of currency don't exist. In Capitalist economies, prices are decided by the market mechanisms of supply & demand. In marxist economies, these mechanisms don't play a role. Going back to the problem at hand, when first beginning to build a railroad, the first question that needs to be asked is how many rails need to be put? If too many rails were used then the railway would waste building materials & other resources. If too little were built, you'd be wasting resources on moving passengers & goods in other vehicles, such as an automobile, which are less efficient at doing the train's job. How exactly would one calculate this in a marxist economic model? It's not possible to counterbalance the physical expenses & physical savings to achieve the desired goal of the most efficient railway system, which is what would happen in a marxist economic model. The hours put into labor and other materials needed to build the road aren't able to be quantified as a common unit, being that certain hours are more important than others and determining the importance of said hours would be arbitrary at best. In a capitalist model, prices are what help us determine how many rails need to be built. If the returns of the railway are higher than the costs of building, then we keep building until we reach a point where the costs exceed or equal the return. Without the price mechanism, one would not know the value of the inputs in the production phase, making rational production impossible. It would be impossible to determine the most efficient way to produce a product because value is subjective and dynamic. Prices allow us valuable insight into the value of resources, which is mind boggling complex. This problem is why shortages plague every marxist economy. Check comments for historical examples, case studies & sources.