> Worse, since you own every stock (not really, but close enough), you now have the 500 companies representing about $27 trillion of market cap, and then thousa

> Worse, since you own every stock (not really, but close enough), you now have the 500 companies representing about $27 trillion of market cap, and then thousands more representing only another $8-9 trillion. So any change in the smaller companies is dwarfed by one good (or bad) day of AAPL, AMZN, GOOG, etc (as happened yesterday). > So if you want the whole stock market, buy it in multiple pieces - a large cap, a small cap, and a mid-cap fund. But this only makes sense because you think holding companies based on market sector (equally weighting each sector) makes more sense than just basing it on the size of the company. What evidence do you have that this is a better approach?