If American investors have learned any lesson in the last 25 years, it is to buy shares on the dips. The slide in 2000--2002 may have been longer and deeper than they were used to but normal service was eventually resumed, driving the Dow Jones Industrial Average to a record high on October 1st.

Among American financial commentators, it is almost universally accepted that shares always rise over the long run. And one ought to expect shares (which are risky) to deliver a higher return than risk free assets such as government bonds.

Nevertheless, investors ought also to remember the world’s second largest economy, Japan. Its most popular stock-market average, the Nikkei 225, peaked at 38,915 on the last trading day of the 1980s; this week, nearly 18 years later, it is still only around 17,000, less than half its peak. Buying on the dips did not work either.

Professionals of the London Business School examined the record of 16 stock markets which were in continuous operation over the course of the 20th century. In itself, this selection showed survivorship bias by excluding the likes of Russia and China. The academies found that only three other countries could match the American record of having no 20-year periods with negative real returns.

Other investors were far less lucky. Japanese, French, German and Spanish investors all suffered instances where they had to wait 50--60 years to earn a positive real return. It was no good following the famous advice to "put the shares in a drawer and forget about them"; the furniture would not have lasted that long.

Besides survivorship bias, there is another problem with the belief that stock markets must always go up. Investors will keep buying until prices reach stratospheric(稳定的) levels. That clearly happened in Japan in the late 1980s, and after seven years, it is still not much more than half its peak level.

A significant proportion of the return from equities in the second half of the 20th century came from a re-rating of shares; investors were willing to pay a higher multiple for profits. But re-rating cannot continue forever.

If investors want a simple parallel with share prices, they need only mm to the American housing market. Back in 2005 an economic adviser to the president said," We’ve never had a decline in housing prices on a nationwide basis. What I think is more likely is that house prices will slow, maybe stabilize."

Lots of people took the same view and were willing to borrow (and lend) on a vast scale on the grounds that higher house prices would always bail them out. They are now counting their losses. Investors in equities should beware of over-committing themselves on the basis of a similar belief Just ask the Japanese.

It can be interred from the text that in the recent two decades the share prices of （）

A. China keeps increasing

B. America keeps increasing

C. Russia keeps declining

D. France keeps still