The Wall fell because of a badly prepared note.
The Berlin Wall stood from 13 August 1961 to 9 November 1989, just over 28 years. That evening, Günter Schabowski read out a new travel regulation at a press conference and, asked when it took effect, said "immediately, without delay". It was meant to start the next day. Thousands went to the crossings, and the guards opened them.
Useful: Large systems often tip on a small, unplanned moment once the pressure is already there.
Source: de.wikipedia.org