Why Diversification May Not Make Senseby Philip Fisher
The percentage of investors who own 25 or more different stocks is appalling. It is not this number of 25 or more which itself is appalling. Rather it is that in the great majority of instances only a small percentage of such holdings is in attractive stocks about which the investor has a high degree of knowledge. Investors have been so oversold on diversification that fear of having too many eggs in one basket has caused them to put far too little into companies they thoroughly know and far too much in others about which they know nothing at all. It never seems to occur to them that buying a company without having sufficient knowledge of it may be even more dangerous than having inadequate diversification.