But as the industry expanded into illiquid asset categories, that strategy was no longer practical.

ECONOMIST: Exchange-traded funds

Pouring 50% of your liquid net worth into an illiquid asset class like art is crazy.

FORBES: How to Outsmart the Billionaires Who'll Bid $80 Million for "The Scream"

And on and on it goes, into ever-narrower and illiquid asset classes.

FORBES: Retirement Investing vs. 'Performance Delusion'

Instead they have become a means for hedge funds to speculate on the market throughout the trading day, allowing them to make complex bets on illiquid asset classes.

ECONOMIST: The risks created by complicating a simple idea

They had been disillusioned by poor returns (what would an optimiser have said about property allocations in 1990?) and by the difficulty of dealing with such an illiquid asset.

ECONOMIST: Property��s strong run is not represented in portfolios

Consider that for most family business owners, the business is probably the most valuable, and the most illiquid asset in the marriage, meaning that it cannot be easily sold or exchanged for cash without a substantial loss in value.

FORBES: Divorce Doesn't Have To Kill Your Family Business

Some of that collateral, now mostly asset-backed securities, is so illiquid that it has yet to be unwound.

FORBES: Money & Investing

Most asset managers, though, have suffered through the recession, as investors fled the illiquid products that characterize Blackstone.

FORBES: Why Investors Need A Diary To Track Stupid Mistakes And Brillant Moves