Hello, I see a lot of nice ETFs. I don't see the harm in buying 8 or maybe even 20 of them, rather than putting it all in the S&P 500. If the ETFs are reasonably distributed across geographies, value, growth, small cap, large cap, add in a few sectors of interest that are doing well... what is the cautionary tale here? As you buy more and more stocks, your risk shifts from ideosyncratic to systemic. It seems that something similar would apply to fund diversification.