This also ignores the fact that your average person, until more recently, couldn't so easily invest in the S&P 500, without some big transaction costs. A coupl

This also ignores the fact that your average person, until more recently, couldn't so easily invest in the S&P 500, without some big transaction costs. A couple of factors that make this possible today: 1. Online brokers, starting in late 90s, lowered retail trading fees, made access easier. 2. low-fee, highly liquid, highly competitive ETFs give anyone cheap exposure to the broader market indicators, like S&P 500. So an ROI calculation from the 1970s is mostly academic, but I guess illustrative of what you might be able to get using that same approach over the next 30-40 years.