It has always struck me that Karl Marx’s prediction that capitalism would be eclipsed by socialism and then by communism was a self-denying prophecy: because he made this prediction, and because of the widespread popularity of his (and other socialists’) ideas, politicians and businessmen were moved to act in ways which allowed capitalism to adapt, rather than to die. It seems that the end of communism may have been partly due to similar reflective-system effects.
In her book, Stasiland: True Stories from Behind the Berlin Wall, Anna Funder writes the following about the opposition to the Socialist Unity Party (SED) in the former German Democratic Republic (the DDR):

I once saw a note on a Stasi file from early 1989 that I would never forget. In it a young lieutenant alerted his superiors to the fact that there were so many informers in church opposition groups at demonstrations that they were making these groups appear stronger than they really were. In one of the most beautiful ironies I have ever seen, he dutifully noted that it appeared that, by having swelled the ranks of the opposition, the Stasi was giving the people heart to keep demonstrating against them. (pp. 197-198)
 

NOTE:  A comment about the processes which led to the end of communism in the USSR is contained in this post.
Reference:
Anna Funder [2003]: Stasiland: True Stories from Behind the Berlin Wall. (London, UK: Granta Books).