What we did and did not learn from 9/11

The ten year anniversary of 9/11 is just over and although I am well aware that many people are writing about it, I do feel compelled to do so too, since I have lived in New York City, and in the area of Ground Zero.  I am still shaken when I see the video footage of that day. And I believe so are many people. But the question is, if these pictures only make us think about past events, or if they make us reflect on the here and now. Since 9/11 we have lived under the constant threat that something similar would happen again. And it did, for example in London and Madrid. Although and mercifully on a smaller scale. But that does not make these events any less memorable. But what do we remember? The people that we have lost and the fear we felt that day? Or should we actually remember the feeling of companionship after these events?