Third: The body

Your body needs this.

I know it's a cliche but your body thrives off stress. Setting on a coach cause basically 0 stress. Yet, bench presses, squats, running cause a ton.

Maybe a more interesting example

Astronauts in space lose as much as 1% bone density per month. 12x more than a senior citizen. This because being takes the stress off your bone weakening them significantly.