repost from my posts at /his/
The problem of socialist economy was not output distribution, but input allocation.
During 1930s, while the victory in economic front was significant, there was a sign of problem. With the appearance of new production sectors (due to completion of industrialisation), came the problem of fighting for input (funding and manpower).
For example, the fight between Stalin and Trotsky was the precursor of that kind. Behind the ideological struggle was actually an economic problem. Trotsky wanted to turn USSR into an full military-industrialised country (similar to Nazi) in order to carry out world revolution (expansionist), while Stalin wanted to focus on building a robust autarkic economy that could survive the onslaught of enemies (isolationist). But why didn't they combine both approaches, wouldn't it be better than adopting only one approach? The answer was because of limited resources. If we thought of Stalin faction and Trotsky faction as two socialist enterprises, then it's actual a fight for funding.
Another example was the fight between Lysenko school and Western genetics school in biology. Actually, nothing prevented both directions of research to cooperate with each other, but why they didn't? Because in a condition of limited of resources and manpower, if the Lysenko school gained a new researcher, it meant the genetics school lost a researcher (researchers as rare resources). The winning of one faction meant the losing of another one, in the condition of limited resources. As Lenin had said, we need to see the real economic struggle behind every ideological struggle, without doing so, history is still a picture shroud in mysteries.
In the late 1950s, the problem was even more grave. With the advent of many new important economic sectors (nuclear, plasma, advanced agriculture, computing, rocket, space, etc.) the fighting for funding and input came to new level. Every sectors were important, but who would receive the most funding? After the disastrous failure of Khrushchev in his agriculture experiment, everyone was aware painfully that much resources thrown into a project didn't automatically mean success. The question of how to allocate resources raged fiercely.
Eventually, the Kosygin's reform returned a mechanism of capitalism, that is, funding would be allocated accordingly to the PROFIT indicator. Of course, there were exceptions (military science, education, healthcare, etc.) but it's a beginning step for turning USSR (and also Russia) into oil-exporting country.
In the 1980s, the oil crisis threw USSR into a crisis (which was understandable because they were socdem capitalist economy then). Due to the 2nd world nature of USSR (no colony), social welfare system and evenly distributed economy, it made USSR the bottom in the hall of fame of profitability. What to do, what to do? What happened was history, but I think everyone understand what I want to say here.
What happened to USSR in 1985-2000, was a giant profitability crisis similar to the great 2010s crisis, the solution was also similar, disbanding most of social security system (a profit drain), discarded all unprofitable sectors (deindustrialisation) and finally turned USSR into a oil needle (the most profitable sector)
As Engels had said, mankind made history, but the result most of them didn't turn out to what they wanted