Bonn-Bonns

Some weeks ago I was in Bonn, the ex capital city of West Germany. There you can visit for free the House of history, telling the history of Germany after the Second World War. The most exciting part was about the fall of that wall.

http://www.youtube.com/watch?v=bmNR-AtnGQs&feature=related

All those people passing under the Brandenburger Tor, celebrating the re-union of the country. That came when nobody was expecting that to happen anymore.

...why did Germans stop celebrating?