Two points: we are wired to think short term, and investment research is typically too abstract and/or complicated to make basic points to the average investor.
Here is a nice succinct piece that shows results for a portofolio going back to 1926 comprised of 60% stocks/40% bonds (as represented by the 10-year Treasury):
What Can a 60/40 Portfolio Deliver?
by The Investment Scientist Michael Zhuang.
The results show the hugely important bottom line that the worst 10-year period was +1.8%/year. Think about this: if you are 75 years old or less, you probably have an investment horizon that is at least 10 years long. Most people, of course, have a considerably longer horizon and absolutely need portfolio growth!
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