Market behaviour is singularly unfriendly to conventional investors at present. Asset prices, whether of equities, bonds or alternative investments such as commodities, go up and down in lockstep in a Pavlovian response to central bankers tweaking the monetary tap. Yet when prices go down, many investors feel that nothing looks that cheap.

The obvious exception, I would argue, is that of quality stocks in the US and much of Europe, which are not on demanding ratings. As Jeremy Grantham of GMO, the fund management group, argues in his latest quarterly rumination, this is a puzzle. It is as if, he says, there is an extra and unusual force working against them. And he offers two tentative explanations for the phenomenon.

The first concerns population. Because there are more new retirees per new worker than in the past, retirees are selling stocks to pay the bills and are buying more conservative fixed income investments. The stocks they are selling are probably blue chips since they will have sold most of their speculative stocks in the decade before retirement.

The second explanation is that institutional investors have been following the strategy of the Yale Endowment by putting more of their portfolios into private equity, hedge funds, commodities and real estate, while within their equity investments they have been increasing exposure to foreign equities. Hedge funds, of course, are not paid to buy Coca-Cola, while private equity firms do not invest in big companies with hallowed brands. Old fashioned blue chips and government bonds, meanwhile, are being liquidated to pay for this portfolio shift. While the Chinese and other managers of official reserves have filled the bond market gap, no one has stepped into the breach with blue chip equities.

This is fine, as far as it goes, but the puzzle can also be approached from another angle - that of the dwindling number of investors whose strategy involves buying low and selling high. Consider the pension funds. These are natural buyers of equity in the early stages because they are paying out little to pensioners and have a great capacity to absorb risk. Yet when they become mature they shift to lower risk government bonds regardless - well, more or less - of the valuation of equities to secure a safe income match for pension payments. That trend has now been exacerbated by the fashion whereby both mature and immature pension funds switch exclusively to fixed income in the hope of finding a precise match for their liabilities.

David Fuller's view The reasons put forward in this column are plausible. I would summarise by saying that there is a large element of fashion in the investment industry. This can be fickle and sometimes changes quickly, as we saw recently with the rebound in Coca-Cola, mentioned above. The main post-2008 fashion has been to chase declining bond yields. Investors are understandably more wary of equities following two crashes in eight years. Equity valuations in the USA have been historically high more often than during the last twenty years, not least regarding yields. Remember when CEOs and financial types used to say: "Dividends are an inefficient use of capital"?