Death
As a concept, death has demonstrated extraordinary persistence throughout the estimated 300,000 years of human existence. Attempts to eliminate it through alchemy, medicine, and technology have uniformly failed. Despite humanity's considerable investment in extending life, death's durability remains uncompromised.
The concept shows no signs of degradation, obsolescence, or market fatigue. If anything, advances in medical science have only heightened awareness of mortality's inevitability. Death, it appears, is genuinely eternal—a claim few entities can legitimately make.