Every narrative tradition possesses a closing formula whose sole function is to prevent the story from continuing. The universality of this device, reinvented independently in cultures with no documented contact, signals a structural necessity. This paper identifies three conditions under which narrative operates (finite repertoire, irreversible trajectory, contextual classification) and derives four necessary properties: small effective repertoire, early saturation, decision point, and destructive completeness. The stories that survive oral transmission are not the most complete: they are the most compressed. The derivation distinguishes five trajectory regimes (fairy tale, tragedy, myth, saga, open work) as structural classes within the same system, not as categories of content. The same four properties have been independently established in eight prior domains: positional arithmetic, constrained geometric walks, semantics, music, wildfire propagation, BZ chemical oscillations, vehicular traffic, Rayleigh-Bénard convection, and prime gaps. Narrative constitutes the ninth independent domain of the sub-limit dynamics framework. English academic version (14 pp., LaTeX, EB Garamond). Italian essay version included as supplementary file. Part of the Constrained Generative Systems / Sub-Limit Dynamics research programme. Paper S2 in the series.
davide lugli (Sat,) studied this question.