> But if I push it out only 1 year (9/2002 to 2/2010) the return is +25%.

Which is kind of my point: many people are looking at the last ten years and seeing that equities/S&P 500 can do no wrong. But things were painful in the previous decade. But then pretty good again in the 1990s.

See Index Fund Advisors' recent ~15 minute video "50 Year Market Review":

* https://www.youtube.com/watch?v=M82Veytnsfw

A lot of people are dumping money into $SPY and and $QQQ, and that's certainly worked recently, but may not work all the time, especially if you have another few decades to go until retirement (which is many/most people's primary long-term financial goal is).

> Which is kind of my point: many people are looking at the last ten years and seeing that equities/S&P 500 can do no wrong. But things were painful in the previous decade.

I will posit that 40 years is probably a bulk of the average person's investing years (25-65), and I may be being generous in "average" based on how often I read people do not invest (if true).

40 year (1980-2020) chart for VFINX (Vanguard S&P 500) - a share was $20 in 1980 (~$63 adjusted for inflation 2020); trades at $320 today. Using a random historical rate of return calculator[1], $10k one time invested in an S&P 500 index in 1980 is just shy of $238k at the end of 2019 at 8.5% return.

[1] https://financial-calculators.com/historical-investment-calc...

> I will posit that 40 years is probably a bulk of the average person's investing years (25-65)

Except that at 65 (the 'traditional' retirement age) one generally doesn't just liquidate all one's equity holdings.

Best practices is generally to increase bond holdings as one ages, but going all-bonds/fixed income is rarely done as I understand things. Unless you've built up enough cash to simply buy an annuity so that it's now the insurance company's problem, or one has a pension, some form of equity returns are needed.

At 65, most people's average life expectancy can be another twenty years in most developed countries (with a 50% chance of making it into one's 90s), so from start (ending school) to finish (death), that could be 60 years. And that doesn't include a partner that may live beyond you if they're of a younger age, and so would also use whatever resources are left for their own needs.