The Postman by David Brin is more or less about this. Also, credit to the OG fallouts - You do change the world, a lot, but it's mostly incidental to what you were doing at the time. Like you save Tandy from some radscorpions early in the first game, and then she goes on to become President of the NCR. It's less "This guy is the only person with agency" and more that people whose lives you touch while you're passing through go on to live their own lives, but you helped.