Inexorability is the fact of not being able to be stopped, and of not listening to anyone who begs it to change. You use it for slow, hard processes: time, ageing, a machine that keeps going, a rule that will not bend. It is a rare, formal, almost literary noun. Most people never say it out loud; they say “you could not stop it,” or they use the adjective inexorable instead. When a writer chooses this noun, they want the heavy, slow feeling that something will happen no matter who asks it not to. Though actually, it is more at home with processes than with a single rude moment — that job belongs more to words like “cruel” or “stubborn.”