It doesn't.
[I was taught the same thing in the 1970's.] If it were true, there would be no reason why the initial successes could not be compounded: Aggregate Demand creates more demand. True growth creates more growth. This is why socialists believe in "stimulus." It's false.
What command economies -- including Socialism -- actually do is very rapidly consume all assets. Comparatively free market economies, even feudalism and mercantilism, create wealth not all of which is consumed. When Socialist revolutions come along, they spend it all. When it's exhausted, since all of the "growth" was created by borrowed money, there is nothing left to sustain it.
It doesn't.
There is plenty of evidence to show that it does, INITIALLY - Russia went from a feudal ag society to a heavily industrialized one in a decade or so. To do so it used up the capital rapidly, and factories WERE built. It is just that they produced garbage most of the time. Plus, since wealth was not being created the money runs out; thus poverty and stagnation.
If you could take a 3rd world country and socialize it; but just for 6-7 years then privatize the economy you'd probably have a vibrant (or at least decent) economy. This is of course assuming you protected private property and allowed upward mobility.