An English folk verse says, “Remember, remember, the fifth of November,” commemorating the failure of the Gunpowder Plot and ushering in the celebration of Guy Fawkes’ Day. Here in the United States, we too have a “remember, remember” moment, though ours doesn’t celebrate: it mourns. For us, the digits 9/11 are enough to call to mind terror and grief and a nation—and world—stunned by unconceivable violence.It was one of those moments that people wi...