Glenn Greenberg of Brave Warrior Advisers, formerly Chieftain Capital Management, prefers to keep a concentrated portfolio that he calls his ‘defense against ignorance’ according to Guru Focus. He currently holds just 11 stocks even though he has $2.16 billion worth of assets under management. After five years at JPMorgan Chase & Co (NYSE:JPM), Greenberg developed his approach to investing at a relatively small firm whose owner required him to become familiar with every aspect of a company’s financials before making any trades, eschewing even pre-made spreadsheets as shortcuts that prevent investors from becoming truly knowledgeable about the companies they evaluate….