The linked page covers this in detail. The market goes down often, and sometimes goes down significantly for several years! The specific point being made is th

The linked page covers this in detail. The market goes down often, and sometimes goes down significantly for several years! The specific point being made is that there has never been a 20-year period where the U.S. stock market declined -- when comparing the start versus end value of the S&P 500 index, on a dividend / inflation adjusted basis.