It's also why one of the first career mentorship steps I go through with Juniors is calculating their hourly rate with the assumption of 40 hours a week (per the ostensible employee agreement), and then calculating it against the _real_ hours worked per week after taking a position.
You'd be surprised how illuminating that's been to those Juniors, and how much of an imprint it left on those folks as they progressed in their careers. A lot of people in our industry genuinely don't recognize how much they devalue themselves and diluting their hourly rate when they're putting in 60-80 hours a week.