Is it one stat that gets balanced all around? How do you know you didn’t spend all your luck surviving something you didn’t even know about. Does it take into account how the world affects you or just your actions? Maybe it’s a general stat that affects everything by the same amount, which is the framework that goes with the “wow I nearly died, I should buy a lottery ticket”.
Easiest is to determine it after the fact, as a relative value for all the stuff that happens to us outside our direct control.