Comment by nighthawk454

It's worse than that, because S&P500 and Nasdaq100 share stocks. Like all of the MAG7 stocks. So if mag7 stocks dip because they're being structurally sold to buy SpaceX, then the S&P500 goes down too.

Arguably even worse because at least Nasdaq100 would have SpaceX in it that's getting bid up to offset the losses in other stocks. S&P won't have SpaceX right away. So it just goes down.

And the more those stocks go down, the lower their market cap - which means next rebalancing date they potentially get re-weighted again causing a bit more selling, etc. Presumably the companies that can will counter this with more buy-backs to keep their share price propped at an acceptable level (?).