Maybe I missed it, but did the Shockingly Simple Math completely neglect that wages and thus lifestyle typically
increase over a career? And that plausible-savings-rates go up as wages increase, as many lifestyle costs are regressive? [1]
Calling out young professionals for $4 coffees is not only an act devoid of human understanding, it seems to be ignoring that many young professionals can only maintain their higher pay/higher stress jobs because small treats keep them energized and sane. And maintaining those careers, even with such expenditures, makes higher total savings possible. [2]
Similarly the article gives short-shrift to retirement lifestyle. It concedes, in passing, that lifestyle at retirement is fixed based on prior working wages. (By admitting that you need to maintain the lifestyle inherent in your savings rate even after you retire).
But it doesn't spend any time talking about the human implications of that.
Most people would look at a $10/hr-and-saving-nearly-every-penny lifestyle and say "this is not retirement. even if i can maintain this lifestyle after only 10 years of work". They see it as scrimping and saving and deferring joy so that they can ... continue scrimping and saving? [3]
Facing such a situation most would opt to continue working, earning promotions, adding to their nest egg and disposable income level, rendering that "achievement" of early retirement as academic-at-best but utterly irrelevant to their actual life.
This is all why sensible retirement planning starts from defining the desired retirement lifestyle and working backwards from there -- accounting for likely wage increases, the declining impact of necessary spending as wages increase, allowing for reasonable levels of luxury spending [4] and accounting for planned life changes, like a house, spouse and children.
Even in the "early retirement" fantasy that hinges on the notion that after retirement you would simply 'work for yourself' or pursue some creative or personal dreams, the costs implicit in pursuing said endeavors need to be calculated into retirement lifestyle to determine an actual retirement age and thus savings rate.
This is particularly necessary when you're pitching the idea of pursuing those things only at retirement, by deferring any and all possible costs in the pursuit of some maximal savings rate. [5]
Most people typically say something like "I'd like to retire and travel and paint". They'll then do things as crazy as including costs related to preparing for years of travel and learning to paint during their working years so they'll actually be ready for their 'retirement' (also: so that they'll actually know whether or not they'd actually enjoy traveling and painting).
At which point the "live more frugally and retire earlier" approach is, again, revealed to be irrelevant for most, as those preparatory and exploratory costs push down feasible savings rates.
The curves in the article allow for this sort of thing, of course, and one can argue "individuals can simply adjust their savings rate downward to allow for their desired lifestyle". But it still neglects that retirement lifestyle is the fundamental consideration. Further, once the exercise is done and the curves adjusted, the whole notion of retiring all-that-much-earlier is, for most people, exposed as infeasible or unattainable.
Lastly, the math above completely ignores that time is not fungible. That is: skipping luxuries in your 20s is not necessarily equivalent to additional years of hypothetical leisure in your 60s. There are things that can only realistically be pursued at a younger age and their costs can make the high savings rates required for such 'early retirement' dreams largely unattainable.
Which is all to say: Yes, one can attain academic early retirement with a very high savings rate. But the lifestyle before and after aren't going to look like something the majority of people can find happiness in. And once you adjust those to allow for likely attainment of happiness, 'early' retirement generally isn't all that 'early'.
[1] A $4 coffee habit has a bigger hit on savings rate at $10/hr than it does at $25/hr. Ergo many more people can more feasibly attain high savings rates at $25/hr, or more generally, later in their career when their salaries are higher. Pushing for a high savings rate early is silly-to-self-defeating (as it sets easy-to-trip 'failure' conditions that are emotionally demoralizing, particularly to those already demoralized by trying to press their lifestyle expenditures to a minimum).
[2] Earnings from higher stress jobs >>> the $4 coffee habit and $100 bar nights necessary to tolerate said job.
[3] Philosophically: if the pursuit of happiness is largely a function of disposable income and we're reducing disposable income to a point that allows 'early' retirement, then we're necessarily reducing the capacity to pursue happiness in our working life to achieve that goal. But said early retirement is contingent upon maintaining that lifestyle of reduced disposable income, raising the question of when exactly does one get to pursue happiness? Let alone pursue the happiness that was deferred? Talk about your pyrrhic victories.
[4] Budgeting 101:
You budget for things like the $4 coffee, $50 dinner out and $100 yoga classes. Because asking people to give them up in the name of maximizing savings just makes most people miserable until all they give up is the budget. Which is far more dangerous to savings than having budgeted for things like this in the first place.
[5] One doesn't retire early by living on $1000/mo and then suddenly have the money to buy the cameras/mics/etc required to pursue a dream of making documentaries. At retirement you still have to live on $1000/mo. Sure, savings are generating that $1000, but if there was no room in such a budget for gear before there'll be no room after. It's necessarily the same budget. And taking money from your savings to buy said gear breaks the math that sustains the retirement lifestyle in the first place. Even if you take from an unexpected windfall -- you need those to cover over unexpected losses.