The Prague Spring was in 1968 and in 1990 the iron curtain fell. Sometimes these things look like they won't work at first but in the long term they erode existing sturctures and do lead to improvements. That's not to say the Prague Spring alone led to the fall of the Soviet Union, just that these events are often indicative of a brewing unrest and longing for change in the population that doesn't just disappear due to a lack of immediate satisfaction.