"It is the evaporation of common memory, what a society experiences over time, say a time span of 25 years. When a tragedy is new, the wound fresh; everyone knows, everyone remembers. But as time goes on, evaporation makes the remembrance pool smaller and smaller until one day, only the outline remains of those who once knew, experienced, and swam in the waters of what had happened. In our own country, already a full third of population has no memory of the events of September 11, 2001. Solemn commemoration grows more important, the intentional act of holding people in the common memory."