Every year on this day, I read Meg Cabot's post about her 9/11 experience. I think about calling my sister, who was fine, getting sent home early from work because the building my office was in shut down for the day. People talk about how everyone was nicer, kinder, more helpful for a while. There were first responders at the Pentagon and the World Trade Center, and people who weren't officially first responders but showed up to help, that day and later. There was the flight that went down in Pennsylvania. During the Olympics in London, NBC cut away from the remembrance of the 7/7 bombings because they assumed Americans didn't care.
Both 9/11 and 7/7 have become days that babies were born, that people got married, that people just went about their day. And I think that's the most important part, that in addition to remembering these tragedies, we remember to go on. 
Rants About New (and old) Things
