I suspect it's a difference between threshold, tolerance and differences between debilitating injury, damage and/or illness affecting muscle that can be rehabilitated, and problems affecting joints and connective tissues that are more difficult to resolve.

In many years of nursing experience, and caring for older family members, I've seen many examples of folks who can tolerate an incredible amount of pain from serious injuries and illnesses, and those who can barely tolerate mild discomfort from less serious issues. I'm sure some of it is physiological, but much is psychological.

To sum up, again, I dunno. My pain threshold is pretty high. I'm a bit frustrated by the current situation -- being able to handle 20-30 miles on the road bike, but being miserable beyond that point and needing a couple of days to recover. But I know I was frustrated two years ago when I first resumed cycling by the same discomfort and pain after rides of only 1-3 miles, then 3-10 miles, and so on.

At the same time, I can't be stupid and ignore the neck problem. Some stuff doesn't just go away simply because we ignore it or take enough pain relievers to mask the injury.