> The worst 30 year return — using rolling monthly performance — occurred at the height of the market just before the Great Depression and stocks still returned almost 8% per year over the ensuing three decades.
(This number is not adjusted for inflation, but still.)
Nope. That graph is incredibly misleading. Note that the middle color represents 3-7% inflation-adjusted returns after "fees and taxes" (how are those calculated?) and the light red color represents 0-3% inflation-adjusted returns (again after fees and taxes). 6.2% is the claimed average inflation-adjusted return. A lump sum invested for 67 years at 6.2% is something like a 5500% return on initial investment.
Very few start dates yield poor returns over a 20-year period, and fewer over a 25+ year period. Much less 67 years.
I'm also not sure about the methodology of "including fees and taxes," since the average mutual fund fee has been very high until quite recently, despite Vanguard's start in the 70s, and taxes are highly individual. The article is light on details.