Money
Monetary systems have demonstrated extraordinary persistence across human civilisation. The Mesopotamian shekel emerged approximately 5,000 years ago, and while individual currencies collapse with monotonous regularity, the concept of money itself has never seriously been challenged. It survived the Bronze Age Collapse, the fall of Rome, two World Wars, and numerous predictions of its imminent demise. Every revolutionary movement that sought to abolish money eventually found itself printing currency. Even theoretical post-scarcity societies in science fiction typically retain some monetary abstraction.
Ninja
The classical ninja era spanned roughly five centuries, from the turbulent Kamakura period through the Edo period's enforced peace. By the Meiji Restoration, authentic ninja traditions had largely dissolved into historical curiosity. The cultural longevity has proven more substantial, with ninja mythology persisting vigorously in global entertainment. However, this represents conceptual survival rather than functional continuity. No government currently employs individuals with formal ninja training, whilst every government maintains extensive monetary policy divisions. The ninja exists now primarily as intellectual property.