Graham on the DCF Method

I've always liked math and the precision it gives to a solution to a problem. But the math used in a financial projection never made me sit easy. Today I read a quote from Benjamin Graham in the 1920s that explains it well:

"...the concept of future prospects, and particularly of continued growth in the future, invites the application of formulas our of higher mathematics to establish the present value of theh favored issues. But the combination of precise formulas with highly imprecise assumptions can be used to establish, or rather to justify, practically any value one wishes, however high, for a really outstanding issue.... The more important the good will or future earning-power factor the more uncertain becomes the true value of the enterprise and therefore the more speculative inherently the company stock.... Mathematics is ordinarily considered as producing precise and dependable results: but in the stock market the more elaborate and abstruse the mathematics the more uncertain and speculative are the conclusions we draw from them. Calculis...[gives] speculation the deceptive guise of investment" Graham, Benjamin, "The Intelligent Investor" pp 315-21