When I actively managed money for mutual funds, we had limits on both total % ownership and how many days of volume we could own. We were small cap growth, so s

When I actively managed money for mutual funds, we had limits on both total % ownership and how many days of volume we could own. We were small cap growth, so sometimes we could be stopped from owning as much of a company as we wanted because it was too illquid. Passive doesn't care - it buys what it needs to replicate the returns of the underlying. Also, it's well known that if a hedge fund (or mutual fund) is in trouble, they sell more of what they CAN rather than what they want. That's one reason why we always knew who else owned the stocks we did. Index funds have no leeway here. They need to sell - whether there is liquidity available or not. My gut is, there will be much less liquidity available during the next crisis than you'd expect. A lot of "non passive" investment is quant driven, which ends up becoming very homogenous in nature across different firms. Many also have momentum factors in play, where they buy short term positive momentum and sell the reverse. Once again,vthey don't have a lot of leeway for humans to say "this market is different".