Came across a cycling couple in distress the other day when I was like 10 hours into that big ride. Told me they were on their 2nd ride ever and now one of them (wasn't entirely clear who) couldn't switch into their big ring. Really wanted to be helpful but all I could muster at that point was "yeah, that's likely a little beyond roadside fixing, just live with it for now". Wish they'd just have a flat or something.