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U.S. stocks are posting losses for a second day in a row on Monday, as the U.K.'s momentous Brexit vote continues to ripple through world markets. The benchmark S&P 500 (SNPINDEX:^GSPC) and the Dow Jones Industrial Average (DJINDICES:^DJI) (DJINDICES: $INDU) are down 1.72% and 1.40%, respectively, at 1:13 p.m. EDT. In that context, it's worth seeking out the counsel of three billionaire investors with over a century's worth of investing experience between them: Warren Buffet, Howard Marks, and George Soros.

Warren Buffett, CEO, Berkshire Hathaway Inc.

Speaking to CNBC at the end of April, the Oracle of Omaha hammered home the notion that he doesn't let macroeconomic developments interfere with his investing:

I don't think [Brexit] is a good thing, but I wouldn't do a thing differently tomorrow in terms of our businesses or our stocks if [UK prime minister David] Cameron told me he was going to come out for it tomorrow strongly. It wouldn't change anything I did. I wouldn't sell the farm I own. I wouldn't sell the real estate I own. I wouldn't sell my house. I wouldn't buy a different kind of car. And I certainly wouldn't change my investment in businesses, but ... I hope they don't do it.

Howard Marks, co-founder and co-chairman, Oaktree Capital Management

Speaking to Bloomberg Television the day after the referendum, Howard Marks, whose memos are a favorite of Warren Buffett, demonstrated wisdom and humility (my emphasis):

On the futility of forecasts:

I don't believe much in forecasts. I also think that at a point in time like today, it's extremely hard to think you know what the future holds. The most important thing in our business is to know what you don't know and I don't think anybody what the long-term implications of [Brexit] are and we shouldn't confuse ourselves on that. There's no recipe, there's no history for this kind of development, so I don't see how anybody can be confident that they know what it means.

On the impact of Brexit:

I also think there will be a psychological effect, as people pull in their horns and spend less and invest less, but I'd be surprised to learn that this is a long-term fundamental negative for these countries.

The reaction is very strong in the markets, but the question is: Are people are going to live differently? Are people going produce less and are people going to buy less? ... Even when there are crashes in the stock exchange, the people outside are still buying hot dogs.

Other than psychological contagion -- which should not be underestimated -- I don't think that this is a fundamental catastrophe. Now, I do think that there will very strong societal, and political, and geographic ramifications, but I have trouble viewing it as a financial catastrophe.

On how not to react to Brexit:

["Sell first and ask questions later"] doesn't sound like a very clever or stable position. There's an old saying I've heard for many, many decades -- as long as I've been in this business -- that markets abhor uncertainty, and they do. But I think that doesn't make them necessarily correct in their abhorrence. So what it means is that when uncertainty rises, people get uncomfortable and, yes, they do sell. But that doesn't make them right and I don't see why increased uncertainty in itself makes selling the right thing to do. It's always a matter of what are you selling, at what price? What are the things that might happen? What are their probabilities?

The mere fact that uncertainty has increased doesn't mean that it's time to sell ... I just don't understand the math through which increased uncertainty means that you should sell and certainly not that you should sell at any price.

George Soros, founder and chair, Soros Fund Management

George Soros is sometimes referred to as "the man who broke the Bank of England" for reaping $1 billion-plus on a bet against the British pound when the currency was forced out of the Exchange Rate Mechanism in 1992. Writing at Project Syndicate two days after the referendum, he paints a bleak picture (my emphasis):

Now the catastrophic scenario that many feared has materialized, making the disintegration of the EU practically irreversible. Britain eventually may or may not be relatively better off than other countries by leaving the EU, but its economy and people stand to suffer significantly in the short to medium term. The pound plunged to its lowest level in more than three decades immediately after the vote, and financial markets worldwide are likely to remain in turmoil as the long, complicated process of political and economic divorce from the EU is negotiated. The consequences for the real economy will be comparable only to the financial crisis of 2007-2008.

Contrary to 1992, when he was short the pound, Bloomberg reports that Soros Fund Management was long the pound going into the Brexit referendum. The pound fell 8% last Friday, according to data from Bloomberg, achieving a 31-year low in the process.

Soros will have done rather better on two positions he held at the end of the first quarter (assuming he was still holding them on Friday). During the first quarter, Soros Fund Management bought call options (a bullish bet) on 1.05 million shares of the SPDR Gold Trust ETF. The family office also more than doubled its put option position (bearish) on the SPDR S&P 500 ETF, which tracks the benchmark S&P 500 index of large-capitalization U.S. stocks, giving it the option to sell 2.1 million shares, up from one million at the end of last year.

Quote of the day

I don’t attempt to predict, I attempt to understand. -- Taylor Mann, founder, Pine Capital

Mann is a 26-year old hedge fund manager based in Larue, Texas (population: 2,962). Less than three weeks ago, he posted a report recommending shorting European financials on SumZero, a social network for professional investors.

Alex Dumortier, CFA, has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Berkshire Hathaway (B shares). The Motley Fool recommends Oaktree Capital. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.