Many of us watching the inferno at Notre Dame de Paris felt that 9/11 dread. This week, as nearly 18 years ago, the news channels kept looping the same horrific video of towers collapsing. At the end, the medieval cathedral remained mostly standing while the twin towers at New York's World Trade Center vanished into a pile of smoking rubble. The outcomes may have been different, but both calamities showed that what we think most permanent may not be.