That's not necessarily true in the land of derivatives. A derivative is a bet on the change in value of something. Essentially hedge funds would build a market

That's not necessarily true in the land of derivatives. A derivative is a bet on the change in value of something. Essentially hedge funds would build a market for a crap asset and then use derivatives to bet that the value would go down. So while the position was short, assembling it drove the bubble up higher.