Most people have no concept of how an automatic transmission works yet they know how to drive a car. You don't have to study physics to understand the laws of motion to drive a car. You don't have to understand any of this stuff to use Macintosh.
So I've broadened the fitness concept to make it one of moderation and balance.
The concept of two people living together for 25 years without a serious dispute suggests a lack of spirit only to be admired in sheep.