their points seem intuitive, but still I'm curious about the different between a low-stress life and an active life. I think it's hard to distinguish between what gives us energy to keep active and what gives us stress that makes us active as a reaction. Would you say it comes down to pleasure? If your activities give you pleasure or satisfaction, that balances the stress of them?

same for retirement-age rock-climbers! they always warmup & stretch, employ the muscle memory and knowledge of optimal pace, time of day, temperature, body weight, breakfast, etc. whereas newbies (like me) mostly rely on limb strength.