Some of the most fun I've had outdoors with friends is when they want to try biking (or bikepacking) with me. You're right that people generally have no understanding of what they're capable of (and that no herculean effort is required).

I suspect that some of this is a result of humans being increasingly unable to estimate true distances. In my city, it can take 45 minutes to drive 3 miles, so most non-bikers understand 3 miles to be an insurmountable distance.