I get the spirit here but not sure I agree that it MUST be true mathematically.
A full time job is 32+ hours a week. Even if I use the American 40, that’s still only 23% of the week not counting vacation or holiday.
Most people don’t get more then 8 hours off sleep a night. That’s 1/3 the day. 43% of the week for everything else.
That’s enough time for you to do something more than sleep or work. Then count in time for vacation and holiday and if you don’t sleep eight hours every night. And if you do stuff at work that isn’t necessarily in your job title.
Due to my meds I can only sleep 4-5 hours a night.