Not only that, but think of all the cultures/jobs where it is normal for people to work much more than the typical 40 hour work week we are accustomed to. Do 18 year old Vietnamese fishermen working 80 hour weeks suffer from "ego depletion" the same way 18 year old college students do in the US? Probably not. It may be an element of our culture / upbringing that we put more emphasis on leisure, and not some psychological or neurological "need".
One of the factors of ego depletion is decision fatigue. If the fisherman does not fish that day, he and his offspring go hungry, and if that decision is repeated they will starve to death. So not really a decision, not one that a rational being would make. If the web developer goofs off on reddit today, instead of looking for new contracting work he won't go hungy.. He can probably coast for a little bit.. Actually, he could potentially just go on welfare, but then he'd have to live in a worse part of town. If he moved in with friends he could work less hours a week and have more leisure time, etc. Lots of choices to make.
Novelty is another ego depleter. The fisherman has done it day-in-day-out for years, probably his father and grandfather as well. It's muscle memory and he's on autopilot. The web developer is constantly novelty fatigued, learning new clients' environments and the latest web framework fads which change month by month. His day has no routine.
As a contractor it is much more difficult for me, and probably I'm the most lazy and restless after coming off a project, with a decent balance in the bank. I am much more focused and mentally sure when the bank balance is low and I'm chasing down business because if I don't find something it'll get uncomfortable quick.
Contrast that to when I was in the gulf of Papagayo, miles from shore, on a small sailboat in the middle of a storm. There was no ego depletion. I never thought 'well, should I continue battling the sea to keep this boat afloat and going to my destination?' There's no ego there, only survival.
Does the Vietnamese fisherman have the harder life by most metrics? Absolutely. However there are downsides to the modern western world.
I don't think cold water is actually bad for digestion.
It turns out that I get more done, run faster, and find both intellectual and physical work much easier when I've taken excellent (rather than merely okay) care of baseline needs like sleep, nutrition, exercise, and household chores.
Willpower as a finite but manageable resource is a much more useful belief than willpower as a character trait.
The idea that you should intertwine focused thinking with unfocused thinking (and/or relaxation) was the subject of Daniel Kahneman's excellent book Thinking Fast and Slow.
It makes about as much sense as believing that your leg muscles are at risk of being depleted, and deciding to avoid exercise for that reason.
If anything, ego depletion proposes that intellectual work is more like exercise than we might otherwise think.
It's up to you to decide whether each situation is closer to "training for a marathon", or "too tired to do stuff".
Our brains have evolved to minimize energy use and all the faculties they manifest: attention, will-power, imagination, creativity, critical-thinking, decision-making etc are parts of a finite budget of energy (glucose), and other resources like metal ions, enzymes & RNAs.
Thinking of will-power as an unlimited resource is a vestige of spiritual-thinking which denies the mechanistic nature of the brain.
There's another way in which will-power is constrained though: the inherited set of parameters that control the rates of production of neurotransmitters. Some people simply cannot ever achieve the levels of focus that others can, no matter how hard they try.
In terms of parameter inheritance - is there science on this? Are some humans predisposed to have less will power than others?
* Wikipedia provides a good summary of replication attempts: https://en.wikipedia.org/wiki/Ego_depletion#Reproducibility_...
* Slate covered the topic here: http://www.slate.com/articles/health_and_science/cover_story...
* And here is a recent, large replication study: http://journals.sagepub.com/doi/full/10.1177/174569161665287...
As a result, I would hesitate before using "ego depletion" as an excuse for rationalizing a lack of self-control (eg. giving into "cheat foods" or being irritable/impulsive). Whether or not "ego depletion" is real, science has not yet adequately validated the theory.
Moreover, there is a risk to accepting the theory as true: because one believes in "ego depletion," one can rationalize a lower degree of self-control, which may have been higher otherwise. This creates a self-fulfilling prophecy.
I think it is fair to assume that, given the current research, "ego depletion" is no more than a reasonable hypothesis. It is possible that willpower may not fit the "finite resource" model at all.