He will not be tired at work because of this; minds don't tire, they only need change and sleep. [...]

You're not tired after work. You can and do push yourself for particular events. Every other weekday evening, spend an hour and a half doing something important. You'll soon want more. Make that a priority; take the social cost. [...]

If you are young and energetic, push yourself full time. But on average, six days a week of striving are enough. If you want more, sure, but going back is okay.

While it's probably true that the average person could push themselves to do more, personal experience suggests that taking advice like this literally will quickly lead to burnout.