Most products are not single-lifecycle systems. They are compositions of components operating on fundamentally different temporal regimes — some structurally long-lived, others subject to faster cycles of technological or functional change. Where these regimes are fused into a single lifecycle, transformation in any component propagates into the identity-bearing structure. Replacement follows. This is not a market outcome. It is a structural consequence derivable before the first unit ships. The persistence condition of La Profilée shows that any designed object claiming durability must separate its long-lived identity-bearing structure from its short-lived transformation-bearing structure, connected through defined coupling. This paper derives the full consequence across four dimensions: the structural condition and why it differs from modularity; why the sustainability discourse operates downstream of this condition; the economics of replacement and what the transition to persistence requires; and why the shift from replacement to persistence is structurally inevitable as temporal divergence accelerates. The condition applies to any designed system that integrates components with structurally distinct evolution speeds and claims persistence beyond the shortest cycle — regardless of domain. Where the persistence condition is satisfied, durability, dramatically reduced material waste, repairability, and economic continuity follow as structural consequences.
Marc Maibom (Fri,) studied this question.