Surely this is pretty obviously true for any (US) business person? The S&P 500 represents the top 500 market listed companies, so if you run a company that (within an order of magnitude or two) has the same capitalisation as one of the index companies, then you should expect (on average) to have the same returns as the index. Maybe some people earn a bit more, some less, but they are all operating in the same economy with the same risks and so forth.