Diversification across asset classes. Physical cash is terrible but to an investor, "cash" tends to mean something like t-bills, which over the past century ha

Diversification across asset classes. Physical cash is terrible but to an investor, "cash" tends to mean something like t-bills, which over the past century have done slightly better than inflation. Gold is horrible if you have too much of it, but it tends to do well in equity crashes, so mixing in a little can be helpful. Bonds also sometimes do well when stocks go down, though I think that's more likely when you start at higher interest rates. Commodities can have 15-year bull markets independent of everything else. An investor in Japan would have done fine if they had a lot of foreign stocks. Etc.