The misconception that costs determined prices prevented economists for a long time from recognizing that it was prices which operated as the indispensable signals telling producers what costs it was worth expending on the production of the various commodities and services, and not the other way around. It was the costs which they had expended which determined the prices of things produced.It was this crucial insight which finally broke through and established itself about a hundred years ago through the so-called marginal revolution in economics.The chief insight gained by modern economists is that the market is essentially an ordering mechanism, growing up without anybody wholly understanding it, that enables us to utilize widely dispersed information about the significance of circumstances of which we are mostly ignorant. However, the various planners (and not only the planners in the socialist camp) and dirigists have still not yet grasped this.