People often dream that better technology can solve the world’s most persistent problems. There is, for example, an international movement that wants to distribute cleaner stoves to fight indoor air pollution in the developing world. Reducing carbon monoxide poisoning would have huge health benefits. Yet human foibles can often stymie the cleverest engineering. New research shows that the stoves can have little long-run impact on air quality or health because they are underused and often break. It also shows that, in devising solutions to social ills of all sorts, some humility is in order.