Buffet on diversification
This is one of my favorite investment concepts: "The strategy we've adopted precludes our following standard diversification dogma. Many pundits would therefore say the strategy must be riskier than that employed by more conventional investors. We disagree. We believe that a policy of portfolio concentration may well decrease risk if it raises, as it should, both the intensity with which an investor thinks about a business and the comfort-level he must feel with its economic characteristics before buying into it."- 1993 Buffet's letter to shareholders
See more quotes from Buffet at: http://en.wikiquote.org/wiki/Warren_Buffett