Fox
The fox operates according to its own scheduling preferences, which align with human convenience purely by coincidence. A fox may appear nightly for weeks, then vanish for months without explanation. Fox behaviour follows patterns comprehensible only to foxes. One cannot summon a fox through any reliable mechanism; one cannot predict fox actions with useful accuracy. The fox is, in operational terms, fundamentally unreliable—present when unexpected, absent when sought, behaving sensibly only by fox standards.
Money
Money demonstrates reliability of a different character. A pound remains a pound; a dollar functions as a dollar; exchange rates fluctuate but the underlying mechanism persists. Money operates according to predictable rules: spend it, it diminishes; save it, it remains (inflation notwithstanding). Financial systems may crash, currencies may collapse, but the concept of money has proven remarkably persistent across five millennia. One may rely upon money existing tomorrow even if one cannot rely upon possessing any.