Warren Buffett is ending his run as Berkshire Hathaway CEO with a big deal, but it doesn't compare to his unspoken warning.Most modern investors, and probably most people in general, know about Warren Buffett, the CEO of Berkshire Hathaway (BRK.A 0.77%) (BRK.B 0.78%). But fewer people know the man who helped to train him, Benjamin Graham. Right now, however, is a good time to think about one of value investor Graham's most prominent contributions to Warren Buffett's investment approach. It has had a $344 bi ...