This seems like a good time to remind myself of Seth Klarman's observation: that an index fund, by its nature, must occasionally dump perfectly good investments and buy worse ones simply because they need the latter in the basket that the index represents.

If you are, say, in FSKAX at Fidelity, and suddenly "OAI" lists for a gazillion dollars, you might suddenly be quite overweight in a stock that you don't care for. Nvidia and the rest are already warping such funds.