I don’t think you’re viewing it quite correctly. Reasonableness standards usually exist in order to funnel legal compulsion into a narrower range than would exist without them. It can bracket out behavior that to the average, ordinary, everyday member of that particular community would be extreme on one end or the other. You generally don’t want the law to require people to behave in extraordinarily heroic or extraordinarily cautious ways compared to how an ordinary person under similar circumstances would act. And “ordinary” here is also context-sensitive. What’s reasonable for an ordinary teenager may be extremely impulsive or foolish for an ordinary adult. Or what’s reasonable for an ordinary expert in a field may be wildly dangerous, say, for an ordinary layman.

All that said, though, reasonableness standards exist all over the law and don’t all necessarily serve the same purpose or function exactly in the same way, when you get into the weeds.