When interest rates were high and stocks were bumping the bottom back in 1982, he encouraged all his clients, including David and Wilma Wilson, to buy on margin.

FORBES: Get rich slow

We also have something which is self-managed, which is if you don't want us to do it, or you have opinions, this really started out as a benevolent brokerage firm, was my concept, where I sort of say you can't buy on margin, you have to buy at least 20 or 30 stocks, but you can only pick from this pre-approved list: companies that rank high as cheap and good.

FORBES: Intelligent Investing Transcript

Credit also was used to buy stocks on margin, greatly increasing the market's volume and volatility.

CNN: Commentary: Is it 1929 all over again?

The next time investors in the stock market buy shares on the margin that plummet in value, will we cover those errors too?

FORBES: The Political Class to Prudent Americans: Drop Dead

Maybe another one is to buy one of those instruments on margin and leverage your position, and finally you could have used options to implement the position.

FORBES: 3 Technical Indicators to Start Using Today

However, home ownership in a downturn has one big disadvantage: most people buy shares outright but homes on margin (ie, they put down a small stake, if anything).

ECONOMIST: Home ownership

And second hand bookshops that buy in paperbacks and sell them on at a margin are a form of sharing but they too are not swaps.

FORBES: Swap.com Social Commerce Without The Cash

The market is punishing Dell for a slight miss on gross margin, but we think that provides an opportunity to buy a growing technology company for well below historically normal valuations.

FORBES: Dude, Dell's Margins Are No Big Deal