Working too little doesn't produce results -- you're wasting present potential for creation.
Working too hard burns you out -- you're sacrificing future potential for creation.
So that begs the simple question: How you maximize potential over both the long and short term?
Well, man-hours, no matter how specialised and scarce, is a factor of production, and is subject to the law of diminishing returns, wear and tear, etc...
The difference between purely mechanical factors of production is of course, the fact that humans have both a stress curve and a recovery curve.
I didn't draw in the recovery curve, because it's impossible to do so. Recovery is non-deterministic, subject to the whims of everyday life. Eat something wrong, feel sick, recovery drops. Celebrate victory of your favourite sports team, feel great, recovery increases (or alternatively, get drunk, and blow off a day) Sun didn't shine today, feel depressed, recovery plummets. And on... and on... and on....
Unfortunately, our work output is contingent upon that unseen and very dynamic recovery curve.
Fortunately, the stress curve is a direct feedback mechanism of the recovery curve. That is to say, stress comes some time AFTER impaired recovery.
Our job then as productive beings (you are, aren't you?) is then to figure out how to read the feedback from the stress curve.
Where we want to be is at the green dot, and never get to the red dot. Once you push stress too high, recovery may take an indefinite period of time. But keep it at the green dot, and you can literally coast for an infinite period of time. In mechanistic terms, this is the point where (recovery rate == stress rate), and the production system is in "equilibrium"
Where it gets dangerous is in the zone between the green and red dots. In this region, we don't know whether or not we are recovering adequately or digging ourselves deeper into a hole. It's the period where your work out is stupendously high, motivation is incredibly high because of that, but at the same time you're getting short bouts of the "I'm doomed" feeling, along with possibly some physical symptoms.
Why staying in this zone is dangerous is because you will hit that red dot hard and fast. It will literally be an issue of "You're hot until you're not" -- A single aspect of work goes wrong, and things spiral into oblivion in the matter of days.
Getting the balance right is not easy obviously. There is a whole host of pragmatic concerns that require knowledge of the specific work environment to address. Sometimes it may be impossible to take a break, sometimes your work explodes into an erratic schedule, sometimse your work environment may be oppressive.
Whatever the case, it is always possible to monitor a Lack of Recovery.
Keep that statement in mind: we are looking for an ABSENCE of recovery, not a PRESENCE of stress.
Note that Humans are woefully bad at figuring out the absence of something - we tend to try and attribute causes and explanations to phenomena, rather than trying to figure out ways to increase resilience to those phenomena. I cannot stress this point enough, that we are trying to ENSURE recovery, and not to AVOID stress.
But to measure an absence of recovery, we need a set of recovery metrics. This is where the experimentation begins. I have no answers for the reader.
I have some metrics for myself, to name a few: Resting Heartrate, Waking time, Sleep Hours, duration of morning "Brain Fog" (I work best at night, but can also work in the morning, but only after X minutes), Weights room performance (specifically, volume tolerance), Absence of urge for Siesta, decreased anxiety when faced with unpredictable problems, finger dexterity (typing speed, guitar picking speed, palpability in guitar fingerstyle technique), etc...
While some are quantitavite, the objective is to derive qualitative measures which have an empirical impact of my ability to produce good work on any given day.
I haven't even gotten into the process of accumulating those metrics and figuring out signal from noise, but that will have to wait for another (long) post.
For now, the key takeaway is that focusing on the Work and the Stress that comes from working is not a good way to ensure future productivity. Instead, we should be focusing on enhancing our rate of recovery to work, and to measure work volume with regard to capacity.
And to remember the old adage: What doesn't kill you makes you stronger.