When I had physical jobs in my youth, I'd come home exhausted. My father told me to get a good 8 hours of sleep, and I would be fine for the next day. When I moved into a career where I used my mind (Engineering and Design) my father also taught me that I needed a different type of a break to rest my mind. It took me decades to recognize his advice. Two different types of muscles. Two different kinds of rest.
Both equal, and important lines of work.
Big digging isn’t just physical work it breaks their mind because after the first few pokes at the hard impenetrable ground they are convinced that the task of digging so deep and long is impossible, and they quit when they see how little they’ve done in an hour or two.