Not too long ago, there are talks that the markets have been hard-carry by the largest capitalized companies in the United States. The worrying thing is whether this is healthy or not. I think over the years, Dimensional Fund Advisers have a few good research piece on this. (Read my comprehensive introduction to Dimensional Fund Advisers here) The largest holdings of the MSCI World index is currently Apple, Microsoft, Amazon, Facebook and Alphabet. Together they make up 13.5% of the index. This is not too concentrated. However, if we peep at the S&P 500, these 5 make up 22% of the index. These index are market capitalization weighted, which means as certain companies get stronger, their share price perform better, they get bigger, their returns drive the returns more. Weight of the largest stocks by market capitalization in the US market from 1927 to 2019 Some companies stay on top for a long time:...