Why you had to take off your shoes while going through airport security

From 2001, al-Qaeda staged a series of plots to bomb transatlantic aircraft, each more surreal than the next—one involving plastic explosives stuffed in shoes, another in a man’s underwear, and a third in soft-drink bottles. Each plot was a spectacular failure, but authorities imposed ever-stricter measures, partly to reassure the public they were doing something. Today, there are new questions about the plots, but also about whether the security response was actually useful.