The rehabilitation of Lycée Fresnel in Paris reveals the tensions hidden behind contemporary celebrations of adaptive reuse. Through the transformation of a 1957 school building designed by Roger Richez and Michel Raclot, this essay argues that reuse is less an ethics of preservation than a practice of negotiation. Existing buildings resist through material limits, inherited meanings, regulatory demands and technical constraints. At Fresnel, glass façades, structural capacities and a residual courtyard expose how architectural decisions emerge through compromise rather than resolution. Reuse, therefore, should not be understood as continuity without loss, but as the work of deciding which contradictions can remain inhabited.