In the decades since Graham first warned against relying on mathematical models of the future, those models have become more sophisticated and more available, but not necessarily any more accurate. Brandes believes that forecasting the future accurately is nigh impossible. Fortunately for us as value investors, it’s not necessary. We aim to analyze and estimate the underlying values of existing businesses without making these dependent on specific future forecasts. There are always uncertainties in the future, but buying into these businesses with a significant margin of safety helps reduce the risks of those unknowns.   

Source: The Intelligent Investor: A Book of Practical Counsel—Revised Edition, Benjamin Graham. Updated with New Commentary by Jason Zweig (HarperCollins, 1973, 2003). The margin of safety for any security is the discount of its market price to its estimated intrinsic value.