A quote from "Buffett Talk to MBA Students at Florida University 1998" at
Buffett: The question is about diversification. I have a dual answer to that. If you are not a professional investor. If your goal is not to manage money to earn a significantly better return than the world, then I believe in extreme diversification. I believe 98% - 99% who invest should extensively diversify and not trade, so that leads them to an index fund type of decision with very low costs. All they are going to do is own part of America. And they have made a decision that owning a part of America is worthwhile. I don’t quarrel with that at all. That is the way they should approach it unless they want to bring an intensity to the game to make a decision and start evaluating businesses. Once you are in the businesses of evaluating businesses and you decide that you are going to bring the effort and intensity and time involved to get that job done, then I think diversification is a terrible mistake to any degree. I got asked that question the other day at SunTrust. If you really know businesses, you probably shouldn’t own more than six of them. 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 a 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. All the people I’ve known that have done well with the exception of Walter Schloss, Walter diversifies a lot. I call him Noah, he has two of everything.
You can listen to his talk at:
http://www.youtube.com/watch?v=P-PobeU4 ... re=related