This is a fundamental problems with games set in worlds defined by a single story, whether that world is Camelot, Middle Earth, or Westeros. If the player characters are not central characters to that story, they are bit players, and feel like bit players. If they are central characters to that story, then they will change the story, which is also a problem. <
This can work in the game's favor. I played in a Pendragon game run by Greg Stafford for a few years, creating characters who aged, married off their kids, etc, establishing their lives in Arthurian Britain as "bit players', tho' ones of some local reknown.
One year, we gathered at Camelot for the annual Christmas feast. All the big name people were at the main table in the inner room. Those of us of lesser renown were at lower table in the outer chamber. Many people of greater importance passed us by, heading to the main table... including an old man with a walking stick and a knight who's cowl hid his face and cloak hid his coat-of-arms. We didn't think much of it. People unknown to us passed by all evening.
At one point, while we were busily engaged in arm wrestling, exchanging rude jokes and comments, and other behaviors suitable to our rank, the inner doors burst open, filing the room with light. Out walked Merlin and a knight who was now clearly revealed as Galahad! Between them floated the Holy Grail!
"That's the Grail!", a player shouted. Another said, "It's the Grail Feast! We're at the Grail Feast!" And for a moment we - the players - were at the Grail Feast. All those years establishing the reality of our characters through mundane things like managing our estates and jousting with friends led us to establishing the reality of this intrusion of the truly supernatural. It was a moment I still treasure.
Greg once said to me that "role-playing games are the only place in the modern world where we can participate in our myths" and it's true. But it was being a "bit-player" in the world of Arthur that made the "central story" real.
On a different note, but still related to Pendragon...
I just reread Gerald Wylie's article on Purgatory in Sub Rosa issue #21. Regarding the Seven Deadly Sins, he observes:
"The concept of a group of inimical sins or vices can be found in ancient Greek thought, notably in Aristotle’s Nicomachean Ethics. He defines a number of human virtues, but he characterizes each as a spectrum at the extreme ends of each can be found negative vices. The common example being courage; too much courage makes one rash and impulsive, whilst too little makes one cowardly. ... If purgatory is likely to play a part in the saga, then players may like to collect and collate the sins and vices of the characters playing a part in that saga. This need not be an exhaustive list but a summary of the kinds of vices that the character has indulged in before and during play."
Pendrgon's system of opposed traits came to mind as away to track something like. As it currently stands, the opposed traits are:
Chaste/Lustful
Energetic/Lazy
Forgiving/Vengeful
Generous/Selfish
Honest/Deceitful
Just/Arbitrary
Merciful/Cruel
Modest/Proud
Prudent/Reckless
Spiritual/Worldly
Temperate/Indulgent
Trusting/Suspicious
Valorous/Cowardly
As a character's score in one goes up, the score in its opposed trait goes down. It might suit Ars Magica more if this was framed as a set of traits like Aristotle's ethics, with being in the center being the goal and providing a bonus, while moving towards either end - rash/impulsive vs cowardly gives a negative modifier. This would be an appropriately Aristotelian way of looking at this in Ars Magica.
I confess that I haven't worked this out more than this. Just a thought...