Inv: Is diversification another failed another failed market theory? market theory?

http://www.usatoday.com/money/perfi/columnist/krantz/story/2011-08-29/Is-diversification-another-failed-market-theory/50181132/1?csp=34money&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+UsatodaycomMoney-TopStories+%28Money+-+Top+Stories%29&utm_content=Google+Reader

Diversification only makes you "feel safe", because you don't know what the stocks will perform. If you are really sure after throughout study, and buy with Safety of Margin. You don't care diversification at all, that just affect your return.
And, as individual, we can trace so many stocks, 10~15 is the max.
And, if you want diversification, just buy in ETF.