The Completion Paradox: Civilisations that achieve sufficient harmony and ecological balance lose the evolutionary desperation that produces detectable, outward-reaching behaviour. Completion and detectability are therefore mutually exclusive states. The silence is not absence it is the signature of success. This paper presents the Sufficiency Equilibrium Hypothesis as a philosophical framework offering a novel resolution to the Fermi Paradox. The hypothesis proposes that civilisations achieving sufficient ecological equilibrium and biological security necessarily lose the evolutionary pressure that produces detectable, outward-reaching behaviour. Sufficiency equilibrium and detectability are therefore mutually exclusive states. The silence of the universe is not evidence of absence but the signature of evolutionary quiescence. This argument draws on existing literature in evolutionary biology, astrobiology, epistemology, and the critique of anthropocentric bias in the Search for Extraterrestrial Intelligence (SETI). The hypothesis is presented explicitly as a philosophically coherent framework rather than a testable scientific theory. Its limitations are engaged directly rather than merely acknowledged, and previously unacknowledged weaknesses are introduced and addressed in full. Conditional predictions are proposed that distinguish the hypothesis from pure unfalsifiability. Terminology has been revised from the original draft to remove romanticised framing: "completion" has been replaced with "sufficiency equilibrium" or "evolutionary quiescence" throughout, reflecting the value-neutral character of the evolutionary claim.