"No one should ever work more than 40 hours a week!"
"Productivity beyond 4 hours a day is impossible!"
Why must I shackle myself to these seemingly arbitrary limitations that other people have? If I'm having fun coding something for 8-10 hours a day, 5 days a week, and I feel I can sustain this output, why do I have to limit myself?
Maybe I (or someone who's able to do this) can just work harder than you (or someone who can't do this). What's the big deal?