Comment by taneq
The human body (like most fit organisms) is antifragile. It needs to be challenged. In this context, people who think "ooh that hurts I'll never do that again" and carefully avoid discomfort find that, by middle age, they can't do anything, and everything hurts. Meanwhile people who think "ooh that hurts, I'd better practise it until it doesn't" are still fully functional into old age because they push their bodies in the right way, and so their bodies stay strong.
Don't get me wrong, the latter group still hurt. Getting old sucks. But their bodies work.
The right level is hard though. I know more than one old person who spent time in a hospital because they thought they could do something they couldn't and broke their bone. "For $20 they would install the new dryer, but no we thought we could do it and that is how my foot got broke in the fall". You should have a cane handy when you need one, but don't use it if you don't need it.
I have no idea how to find the right balance.