Besides other problems that USSR had, like the pervasive corruption and the lack of incentives for taking initiative in almost anything, it's worth considering that it achieved economic development by large scale investments. That meant huge farms, huge factories, huge everything please! The good was the immediate results of the said investments thanks to the good (enough) efficiency as the economies of scale kicked in. The bad was in the costs required to keep those damn behemoths competitive as the world evolved! Factor in the fact that the declared reason behind those huge investments was not economic efficiency but employment of people, and you get something that will have trouble in the long term keeping up with their counterparts in the capitalist world. That was short-term (political) capital seeking policy at its best! That however, mattered less because usually it was just about some bureaucrat's career bet for getting results fast, cashing out in time the political merits, and then exit by propelling himself to another position somewhere, a game played up to the highest levels (e.g. Leonid Brezhnev and Virgin Lands Campaign). The ending question is, does China differ in this regard?