Scott H Young

Parkinson’s Law states:

“Work expands so as to fill the time available for its completion.”

This “law” was proposed by the British naval historian C. Northcote Parkinson in a satirical 1955 essay for The Economist. Taken literally, it’s obviously false. Simply setting a deadline doesn’t make a goal achievable on an arbitrary timeframe.

There’s a heap of academic literature making the opposite case. The planning fallacy describes the well-documented tendency for complex projects to have cost overruns and delays. Indeed, the truth is perhaps closer to Hofstadter’s Law, where the author Douglas Hofstadter argued tongue-in-cheek that, “It always takes longer than you expect, even when you take into account Hofstadter’s Law.”

Despite its definitively un-lawlike empirical status, Parkinson’s Law does capture an essential human truth: when we loosen time constraints, the time needed to do something somehow expands to fill at least some of the gap.

Energy, Pacing and the Limits of Human Endurance

I was thinking about Parkinson’s Law as I was reading Endure, Alex Hutchinson’s excellent book examining the limits of human persistence and some of the scientific controversy as to the exact nature of those limits.

Hutchinson, an impressive endurance athlete himself, retells a story of trying to beat his personal best time in the 1500m race in his days in track and field. He notes that despite giving every bit of effort he could muster, his pace would always speed up right at the end. He even tried to “trick” himself into running flat out, but consistently found the same dip in speed in the middle of his races.

If we assume that endurance is limited primarily by the body’s internal resources—muscle glycogen, oxygen uptake, ATP and whatnot—this makes no sense. If we’re giving it absolutely everything we’ve got, how is it possible that we can speed up as the race reaches its final stretch?

Hutchinson wasn’t alone in his peculiarity, however. It turns out that world-record runs show the same pattern of a dip in pace followed by a slight acceleration toward the end of the race. Even the most well-trained, disciplined and motivated runners must be holding something back.

Phenomena like this suggest to some academics that the true limits on endurance are not physical, but in the brain. Runners like Hutchinson don’t top out because they reach their true physical limits, but because the brain throttles performance so they never risk reaching those limits. This gives a comfortable margin to prevent bodily damage, and it anticipates future requirements for performance, holding back some when the race is still far from over.

The Connection Between Physical Fatigue and Mental Energy

The presence of a “central governor” that throttles athletic performance makes evolutionary sense. If we run so hard we tear our muscles, break blood vessels or starve our brain of oxygen, it doesn’t matter that we just set a personal best.

But do the same rules work for mental fatigue? After all, nobody’s brain starves of oxygen because they stop procrastinating.

The links between mental and physical fatigue are interesting. Participants who perform difficult mental tasks and then do an endurance test on an exercise bike give up earlier than those who haven’t done hard mental tasks. Mental performance is generally enhanced by exercise, but our performance typically suffers when we try to do cognitive tasks while exercising.

Some scholars even argue that physical and mental fatigue are the same thing. That, while there are certainly different facets to the phenomenon (e.g., being sleepy, muscle weakness, etc.), there is a general component of fatigue that seems to encompass both physical and mental work.

It’s not yet clear what the function of mental fatigue is. It’s possible that, like physical fatigue, mental fatigue is tracking some underlying biological state: energy availability, local sleep debt or stress hormones.


Another possibility is that fatigue in general, and mental fatigue specifically, is really about protecting us from investing in undesirable goals. When we work too long at an activity that lacks intrinsic value and is not immediately satisfying, fatigue begins to build. Perhaps fatigue is a more general emotion that creates pressure to change activities—protecting our bodies from physical overexertion in athletics and our limited attention from being absorbed by tasks that seem uninteresting or futile.

In either case, the effect of mental fatigue is similar to physical fatigue: throttle performance to prevent overexertion, both in the moment and anticipating future demands.

Getting More Done by Working Less

I bring all of this up because a key idea in energy management is working within natural rhythms of effort and rest. Work non-stop and we’ll exhaust ourselves. But if we can adopt periods of intense focus with complete recovery, paradoxically, we can get more done in less time with less exhaustion.

I’m certainly not the first to point this out, and the idea that we somehow get more done when we restrict our working hours within natural rhythms is a long-standing finding in productivity literature. From the earliest days when H. M. Vernon found that reducing workloads from then-common 70 to 80 hour workweeks did not result in reduced work output, to modern incarnations like Cal Newport’s fixed-schedule productivity, the paradoxical finding that we’re more productive when we force ourselves to work less has long been a self-help staple.

These ideas on fatigue add an interesting twist to the explanations. If the effort we put into tasks is not simply a measure of our underlying mental capacity, rather a subtle “pacing” strategy our brain is implementing to get through the work, it explains why punishing, non-stop schedules so often lower productivity.

Anticipating that we’ll be unable to rest, we unconsciously reduce our willingness to put in effort. This can mean sticking to the task but putting in less effort and accepting reduced performance. Alternatively, it can mean procrastinating, slacking off or engaging in trivial aspects of the work that are lower effort and less important.

As a result, the time needed to finish the work to a given standard expands, and we get an effect akin to what Parkinson described in his 1955 essay.

What Does it Mean to Manage Energy?

This, I think, gets at the heart of what it means to manage energy. It’s not simply about finding “balance” or making trade-offs between self-care and time for work. Instead, it’s reflecting the fundamental reality that we work best when we have healthy rhythms of work and recovery.

Too often, our culture pits extremes against each other. You’re either an ambitious striver committed to the hustle, or you’re a delicate orchid that must be sheltered from excess stress. Then, predictably, people line up to denounce one side and support the other.

I think what the research I’ve been covering shows, convincingly, is that this is a false dichotomy. Meaningful work, natural rhythms of work and rest, and healthy lifestyle habits like nurturing good sleep, diet and exercise: these practices for managing energy aren’t just key to working hard, but to living well.