Glenn Dubin explains modern portfolio theory: having a collection of managers that are both long and short in the markets enables easier allocation of capital to reach the highest returns with lowest volatility. 
See the video clip here: https://www.youtube.com/watch?v=ZlqPB3uK8wM

Glenn Dubin On Modern Portfolio Theory Highest Return, Lowest Volatility. glenndubin portfolio

Glenn Dubin is an investor and philanthropist. Glenn is also the Principal of Dubin & Co. a New York-based private investment company.