The article deals with the analysis of the mixed economy's architectonics, with the non-market sector as its core. The functional significance of the non-market sector in mixed economy is neglected by the modern market economists. The author suggests a model of the market-in-equilibrium to illustrate the key points of the article.In particular, the author links the mission of a non-market sector in a mixed economy to the compliance between the commodity and the "money surplus" generated in the market sector. The main concern of the effective mixed economy is to provide sufficient financial support for the non-market sector, through the taxation of the private entrepreneurs. The article covers the issues as follows: weak theory cannot obstruct effective practice; "happy" sector of the mixed economy; unseen intrigue of the economy; the main systemic problem of the mixed economy; mixed economy needs market transformation of the non-market sector; the Achilles' heel of mixed economy. The article suggests arguments for economists' interest towards the non-market sector. It is argued that mixed economy's effectiveness (due to its inherent features) becomes the main factor of the economic growth. The author argues that having the non-market sector not included in the mechanism of the mixed economy development, the theoretical framework of the mixed economy is impossible.