We don't know what moments will change our worlds forever. We never see them coming, and we can never fully prepare for them even if we do. 9/11 is a big one. Just think about who's been touched directly or indirectly. It started with the people who died in the attacks and it spread to their families and friends and then to all of us.
9/11 to me, is simply a reminder to treasure the moment. We don't know when great tragedy will strike. Sometimes it's the smallest thing that can lead to major upheaval in our lives. We just don't know. All we can do is try our best to live a good life. Don't lose sight of the beauty that surrounds you every single day. Don't take loved ones for granted. One day, they too will disappear. Don't take your own potential for granted. Don't spend too much time regretting what has or hasn't happened, it's over. What can you do right now that will have a positive impact on your (or someone else's) future? That's all there is. The big events just help us remember.