(New York)

This topic gets thrown around a reasonable amount in the media, but because it seems to defy normal human perception, we wanted to run a story on it—the growing and dangerous level of stock concentration. So what do we mean by that? We mean that three stocks—Amazon, Microsoft, and Netflix, have accounted for almost 50% of all the gains of the S&P 500 so far this year. This kind of concentration plays itself out time and again, whether it be in broad index tracking, or in niche sector ETFs, which end up being hugely weighted to just a few stocks.

FINSUM: Anyone can understand the danger of concentration at the point of purchase, but one of the key points to remember is that time tends to make a portfolio more and more unbalanced as the winners inevitably grab a larger share and the losers less.