As a child sitting in a classroom in Belgium, Nathalie Kühn’s attention kept drifting to the window. Not out of boredom, but out of a question she could not let go: how does it all work? The plane climbing out of sight in the distance was not simply a machine to her. It was the visible tip of an invisible system, thousands of decisions, communications, handoffs, and human judgements converging in real time to move people safely across the world.