This quote reminds me of what Warren Buffett said at the 1996 Berkshire Hathaway Annual Meeting:
"We like to put a lot of money in things that we feel strongly about. And that gets back to the diversification question.
We think diversification, as practiced generally, makes very little sense for anyone that knows what they're doing.
Diversification is a protection against ignorance.
I mean, if you want to make sure that nothing bad happens to you relative to the market, you own everything. There's nothing wrong with that. That is a perfectly sound approach for somebody who does not feel they know how to analyze businesses.
If you know how to analyze businesses and value businesses, it's crazy to own 50 stocks or 40 stocks or 30 stocks, probably, because there aren't that many wonderful businesses that are understandable to a single human being, in all likelihood."
That said, knowing how to analyze businesses is hard, and one should understand what makes them qualified to give up the only free lunch in investing.