When a person is inexorable, they're stubborn. When a thing or process is inexorable, it can't be stopped.

This is a word for people and things that will not change direction. An inexorable person is hard-headed and cannot be convinced to change their mind, no matter what. You can also say that a process, like the progress of a deadly illness, is inexorable because it can't be stopped. A speeding train with no brakes is inexorable; it's not stopping till it crashes. When you see the word inexorable, think "No one's stopping that."

Definitions of inexorable

adj not to be placated or appeased or moved by entreaty

“Russia's final hour, it seemed, approached with inexorable certainty”
grim, relentless, stern, unappeasable, unforgiving, unrelenting
incapable of being placated

adj impervious to pleas, persuasion, requests, reason

“Cynthia was inexorable
adamant, adamantine, intransigent
incapable of change