You cannot know what the future would have been had you not arrived.Ah, but I can and do know that it would have happened whether I was there or not. My presence changes nothing.
Which proves you learn nothing from experience. You were in Columbus, Ohio, the city of your own birth. It was not the same place you had been moments before, and the fact that it was a few years in the future did not explain the differences. That should have alerted you to the fact that being in a familiar place does not mean it is the same place, or that the same events will occur or have occurred. For all you knew, the Japanese might already have had atomic weapons, and been planning to obliterate most of Hawaii. Or they might not be coming. Then again, you could be in something like a holodeck simulation, none of it real at all.
You make your best guess and go with it.
You speak of every other NPC who did not go to the castle--by which I assume you mean the aging blacksmith for whom you apprenticed, his wife, the blind beggar in the village, the children. You do not know how many indigs tried and failed, or died, trying to save the princesses. You only know that no one succeeded. That means you don't know how many lives you might have saved had you taken action before you did.
Yeah, maybe there are players who say, "I see the story, let me follow it." But then, even they wouldn't do it if part of that wasn't also "If I follow the story, I might be the hero."
--M. J. Young