From this Warren Buffett speech at the University of Florida:
"If you can identify six wonderful businesses, that is all the diversification you need. And you will make a lot of money. And I can guarantee that going into a seventh one instead of putting more money into your first one is gotta be terrible mistake. Very few people have gotten rich on their seventh best idea. But a lot of people have gotten rich with their best idea. So I would say for anyone working with normal capital who really knows the businesses they have gone into, six is plenty, and I probably have half of what I like best. I don't diversify personally."
Clearly, this view on diversification is far from conventional. Charlie Munger -- and this is not exactly a surprise -- once said something rather similar in a speech to the Foundation Financial Officers Group:*
"I have more than skepticism regarding the orthodox view that huge diversification is a must for those wise enough so that indexation is not the logical mode for equity investment. I think the orthodox view is grossly mistaken."