Here are two great quotes from Sir John Templeton about the importance of diversifying your investments:

DIVERSIFICATION SHOULD BE THE CORNER STONE of your investment program.  If you have your wealth in one company, unexpected troubles may cause a serious loss; but if you own the stocks of 12 companies in different industries, the one which turns out badly will probably be offset by some other which turns out better than expected. — July 1949

IT SEEMS TO BE COMMON SENSE that if you are going to search for these unusually good bargains you wouldn’t just search in Canada.  If you search just in Canada you will find some, or if you search just in the United States you will find some.  But why not search everywhere?  That’s what we’ve been doing for forty years.  We search anywhere in the world. — November 1979