Abstract This essay examines the “15-minute city” not as a normative urban planning proposal but as an operational system implemented under sustained stress conditions. Rather than evaluating intentions, values, or policy narratives, the analysis focuses on the structural logic that emerges when urban proximity becomes the organizing principle of the entire city. The paper explores how reducing human mobility, discretizing urban space into functional nodes, and increasing dependence on shared infrastructures alter the balance between circulation, autonomy, and governability. Particular attention is given to second-order effects that rarely appear in mainstream discussions of the model: the stabilization of everyday behavior, the decoupling of logistics from human movement, the emergence of nodal urban grids, and the growing role of digital interfaces in regulating access, mobility, and identity. The essay also situates the model within a changing risk environment characterized by biological uncertainty, technological traceability, and increasing pressure for operational resilience. Under these conditions, urban proximity can function not only as an efficiency improvement but also as a defensive architecture that privileges predictability, containment, and administrative legibility. The text does not propose alternatives or normative prescriptions. Its objective is diagnostic: to describe the structural conditions under which the model operates, the incentives that sustain it, and the limits that emerge when urban resilience begins to compete with spatial autonomy.