Time
Time's inevitability represents perhaps the only absolute in physics. One cannot negotiate with time, bribe it, escape it, or pause it. The second law of thermodynamics ensures that time moves in one direction with the implacability of mathematical certainty. Every civilisation has attempted to transcend time's limitations; every civilisation has failed. Even light, the universe's fastest phenomenon, cannot escape time's dominion but merely experiences it differently. The inevitability of time extends to everything that exists, existed, or will exist. Stars burn out, galaxies disperse, and even protons may eventually decay over timescales so vast they make the universe's current age appear momentary. Time does not merely occur inevitably; it defines inevitability itself. To exist is to submit to time's passage. There are no exceptions, no exemptions, no appeals.
Volcano
Volcanic eruption is probabilistic rather than inevitable. Many volcanoes remain dormant for millennia; some never erupt at all. The Pacific Ring of Fire demonstrates concentrated volcanic activity, yet specific eruptions remain unpredictable in timing despite sophisticated monitoring. One can, with varying degrees of success, avoid volcanoes entirely. Populations relocate, monitoring systems provide warnings, and vast portions of Earth's surface remain forever beyond volcanic threat. The volcano's occurrence, while dramatic when it happens, lacks the universal applicability that characterises true inevitability. Antarctica's residents, desert dwellers, and inhabitants of ancient continental shields live entirely outside volcanic concern. The volcano is a powerful regional phenomenon, but its reach remains fundamentally limited. One can conceive of a world without volcanoes; one cannot conceive of a world without time.