Quote Originally Posted by Grey Watcher View Post
The use of the word "determination" in Undertale is a pun. Yes, it means "refusal to give up," but it also means you, being the player, literally determine how the story goes.
I always figured it was meant to echo determinism, as in the philosophical idea that all future events are set in stone by whatever came before them.

Which is both true for the game, and not (because you, the player, have agency over the events of the game, but your actions will always have the same consequences). Which ties super well into the metacommentary the game made on morality systems and choices in games.