The correct answer to this open question is the following.
When Hungary opened its borders, it created a "hole" in the iron curtain.
Hungary was the first country to open its borders on September 11, 1989. This represented a magnificent opportunity for people to leave the socialist countries under the influence of the Soviet Union. That is why historians coined the term "it created a "hole" in the iron curtain." When this happened, thousands of people that lived in East Germany left and went to the Western Europe countries. Socialism had collapsed in Hungary.