Monday
Monday arrives with absolute chronological certainty. Not once in recorded human history has Monday failed to appear at its appointed position in the weekly cycle. This reliability rate of 100% represents perfection in scheduling terms, a consistency that borders on the relentless.
Humanity has attempted numerous countermeasures: public holidays, sick days, four-day work week trials. Yet Monday persists, merely shifting its character slightly whilst maintaining its fundamental essence. The institution remains impervious to reform.
Volcano
Volcanoes operate on geological timescales that render them profoundly unreliable from a human perspective. The average stratovolcano erupts once every 500 to 1,000 years, a schedule that offers little utility for planning purposes. Even seismic monitoring provides merely days of warning at best.
This unpredictability, whilst contributing to the volcano's mystique, represents a fundamental failure in reliability metrics. One cannot schedule around an entity whose timetable spans millennia. The volcano's capriciousness undermines its practical utility entirely.