a lot of people who've had very little illness or injuries in their lives have a very hard time understanding the kind of sickness that can actually keep you from doing something.

Yeah. I've dated way too many of those! Never again! I also know how hard it is on a person like that when a long string of good luck finally ends -- if one hasn't built the emotional endurance over a lifetime, then learning it at (say) age 75 isn't easy at all.