My biggest issue with this type of standard investment advice though is the low savings rate recommendation. The 10% savings rate is really not enough, IMO. If your 10% went only to retirement and nothing more, that's 51 years until retirement (if it's well invested)- minimum age 69. For a <a href="https://www.businessinsider.com/social-security-life-table-charts-2014-3">20 YO male</a>, the likelihood that they will die before reaching age 70 is 19.9%- that's a pretty significant probability that they won't live long enough to reach retirement.
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In reality this standard advice is setting people up for a pretty sad life IMO. And there's no warning or explanation that if they just saved more, they could retire earlier. Maybe I'll just include the "shockingly simple math" article with any recommendation- to balance out the advice a bit.
I suspect the standard advice leans pretty heavily on social security income in addition to personal savings in order to enable retirement. The shockingly simple math post doesn't factor in social security (since it's really not a big factor for those of us planning to retire early). Which is why a lot of people retire in their 60s despite saving only 10%, or even less than 10% of their lifetime earnings.
For a person earning $20,000/year, social security is going to be a pretty substantial part of any plan to retire at conventional retirement ages (60s). Keep in mind that if a person earned the inflation adjusted equivalent of $20,000/year for 35 years they'd receive ~$13,000/year in social security income.
Assuming they paid no net income tax and saved 10% of their income, this hypothetical person's spending would be about $18,000, so they'd only need to make up the difference of those two ($5,000/year) from personal savings or spending reductions once they no longer had to work. That $5,000/year could come from withdrawing 4% /year from a stash of $125,000. Saving up that stash by putting aside 10% of their income ($2,000/year), would take about 25 years (assuming 7% return).
But the bad part about counting on social security for such a large chunk of one's retirement income is that there is really not as much incentive to save more since even if you up your savings by what can feel like a lot to a normal person (going from 10% to 15 or 20%), you still likely won't be in a position where you feel confident retiring before hitting either 62 or more likely full retirement age.