There are no long-term lessons - ever.

Complexity - limits competition.

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.

If another person were to enter the building, it would once again be empty.

When excesses such as lax lending standards become widespread and persist for some time, people are lulled into a false sense of security, creating an even more dangerous situation. In some cases, excesses migrate beyond regional or national borders, raising the ante for investors and governments. These excesses will eventually end, triggering a crisis at least in proportion to the degree of the excesses. Correlations between asset classes may be surprisingly high when leverage rapidly unwinds.

Short sellers age in dog years.

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.