Interestingly, we have beaten the market quite handsomely over this time frame, although beating the market has never been our objective. Rather, we have consistently tried not to lose money and, in doing so, have not only protected on the downside but also outperformed on the upside.

A tipping point is invisible, as we just saw in Greece. In most situations, everything appears fine until it's not fine, until, for example, no one shows up at a Treasury auction.

Value investors will not invest in businesses that they cannot readily understand or ones they find excessively risky. Hence few value investors will own the shares of technology companies. Many also shun commercial banks, which they consider to have unanalyzable assets, as well as property and casualty insurance companies, which have both unanalyzable assets and liabilities.

Investing today may well be harder than it has been at any time in our three decades of existence.

Unlike return, however, risk is no more quantifiable at the end of an investment that it was at its beginning. Risk simply cannot be described by a single number. Intuitively we understand that risk varies from investment to investment: a government bond is not as risky as the stock of a high-technology company. But investments do not provide information about their risks the way food packages provide nutritional data.

There are no long-term lessons - ever.

To achieve long-term success over many financial market and economic cycles, observing a few rules is not enough. Too many things change too quickly in the investment world for that approach to succeed. It is necessary instead to understand the rationale behind the rules in order to appreciate why they work when they do and don't when they don't.