As the scent of burning electrical wire and the pulverized dust settled over Manhattan in the wake of the 2001 World Trade Center attack, a certain book disappeared from New York City bookstore shelves. Within a week, that book rocketed from No. 8,000 to No. 125 on Amazon.com rankings. It described the nature of fanatics, offering a powerful window of understanding into the people capable of blowing up those two towers. "The True Believer" was published in 1951. Its author, Eric Hoffer, was a self-educated longshoreman born in New York City to a German cabinetmaker and his wife. His keen...