It depends how you define "work". Sitting in an office doing what is told for 40 hours is ridiculous and hellish, and it's much of why that system doesn't work.

It depends how you define "work". Sitting in an office doing what is told for 40 hours is ridiculous and hellish, and it's much of why that system doesn't work. People "revolt" by showing up and working at 1/8 speed. If we extend the definition of "work" to include self-directed projects, education and enrichment, 40-55 is about right; 40 for most people and 55 for the more ambitious. Beyond 60 hours per week, marginal productivity is minimal.