Decades later, the Dardennes’ impact on cinematic realism can scarcely be overstated, and they have, to some extent, been eclipsed by their own much revered influence. Their jagged techniques, absorbed by filmmakers the world over, have softened; they still follow their characters about in handheld long takes, but gone is their habit—deployed most radically in “The Son,” their masterpiece from 2003—of zeroing in on the back of a protagonist’s ear. Even so, they have never come close to breaking faith with those essential principles. At the heart of their work is the question of what we owe one another—what decency spurs us to do, and at what cost. In “The Son,” a carpenter weighs the possibility of avenging his child’s murder. In “The Kid with a Bike” (2012), a hairdresser is compelled, by forces beyond her understanding, to intervene on behalf of a young boy who has no one else. The realities of poverty, neglect, racism, and violence are harsh constants in the Dardennes’ working-class universe, but the filmmakers believe no less intently in the persistence of goodness—a force that is all the more powerful, they insist, for the stubborn unpredictability with which it can take root.