Markets, I argue, matter significantly for macroeconomic development. The reason for this strange statement is that policy practice in industrialized market economies is routinely governed by models that ignore the role of markets. Policy makers are therefore at risk of misunderstanding the economic situation and of mismanaging the economy. Some macroeconomic models with sufficient nonlinearities and a production lag, two pioneering articles by Day (1982,1983) demonstrated, exhibit phases of erratic fluctuations (or deterministic chaos). Shortly thereafter Eliasson (1983, 1984) observed the endogenous emergence of similar unpredictable irregularities in simulating a complex, agent based, market self-coordinated economy wide model implemented on Swedish data. The irregularities originated in a failure of markets to coordinate production, employment, and investment decisions as they were pushed excessively by policy to become more efficient. In this agent based model of an Experimentally Organized Economy, called MOSES, progress is governed by a dominant flow of successful business experiments conducted by firms, trailed by a flow of mistaken projects. The coordination of these flows by autonomous market agents was shown to be easily disturbed by external interferences, for instance unwitting policies. Markets, simulation experiments however also showed have great endogenous capacities to restore disturbed order. Large private investment mistakes at the agent level, experiments furthermore indicate, incur only minor social costs if production on the site is promptly terminated, and markets organized to efficiently reallocate resources. Bold private investments should therefore be encouraged, corrections of identified mistakes made without delay, and the efficiency of markets to reallocate resources paid attention to. I conclude that central policy in “Sweden like industrial economies” can only effectively be pursued by taking advantage of the endogenous capacity of functioning markets of effective self-coordination. Coordination failure being created by policy failure masquerading as market failure should be considered before market failure is blamed.