That is a hard question to properly answer, as there are so many different options to look at in terms of failure. One could argue that the USSR never truly succeeded as a country, and thus was failing from the October Revolution. It was never properly consolidated, and lived only because the centre repressed any dissent for seven decades. The ideals of creating a Soviet state and people never happened, and differences amongst the population plagued the USSR the entire time, as was quite apparent when all fifteen republics broke away once given the chance.