Michael Parenti, Blackshirts and Reds: Rational Fascism and the Overthrow of Communism:

The pure (libertarian) socialists' ideological anticipations remain untainted by existing practice. They do not explain how the manifold functions of a revolutionary society would be organized, how external attack and internal sabotage would be thwarted, how bureaucracy would be avoided, scarce resources allocated, policy differences settled, priorities set, and production and distribution conducted. Instead, they offer vague statements about how the workers themselves will directly own and control the means of production and will arrive at their own solutions through creative struggle. No surprise then that the pure socialists support every revolution except the ones that succeed.

For the still meme confused: Survivorship bias

(Stolen from @RoseTintedGlasses@matapacos.dog)