The article develops the topic of current problems of modern socio-economic transformations that require reflection and comprehensive research, which occur both at the national and international levels and encourage the development of an urgent development strategy taking into account the formation of a new world economic model. This article is devoted to the analysis of the potential of theoretical ideas about rationality, which are the basis of the subject of economic theory. The hypothesis is put forward that as the transformation of the industrial economic system, which has presented a demand for a rational "economic man", into some other system, the "economic man" himself must also transform into a new being; otherwise, its effectiveness will either be undermined or lost. There are three stages of this transformation at three levels: individual, national and supranational. The author traced the transition from the complete rationality of the "economic man", guided by a purely market equilibrium, to the pseudo-market (social) equilibrium of the "socio-economic man", and from it to the principle of partial optimization (satisfaction), the criterion of effectiveness of which is sustainability. As a result, the conclusion was substantiated that the "economic man" managed to maintain competitiveness in the XXI century, but only at the cost of a deep transformation of his own from full rationality to limited, from purely economic rationality to socio-economic-ecological. A forecast is made regarding the increase in the rationality of non-economic goals of cooperation, mutual benefit, the coupling of knowledge and technology to spiritual, moral, cultural and ethical principles and norms, which actualizes M.I. Tugan-Baranovsky's prediction about the fate of political economy, made by him more than a hundred years ago.