On the basis of the diary of A.S. Chernyayev (a considerable figure in Soviet and Russian politics, who, in particular, worked for many years as M.S. Gorbachev’s assistant), S.P. Peregudov analyzes the most significant prerequisites of the perestroika and of the “new thinking” policy, which was in the long run followed by the downfall of the Soviet Union. As the basic causes of what happened the author points out, first, the system’s inability to adopt and realize the new theoretical initiatives and, second, society’s failure to accept the new rules.