How can you measure the risk of a share?

For some reason they let the loons out of the mad house in finance a long time ago. These loons came with  PhDs, prizes and all kinds of fancy equations and for the traders who worked so hard in their spare time to get minor letters after their name like MBAs or CFAs they were too much to resist. These crazy fools suggested that the risk of a share could be quantified as its volatility - essentially how much it wiggled around on a day to day basis.   For whatever reason (Emperor's New Clothes springs to mind?), this has been taken as complete gospel by the finance world who have embedded this volatility measure of risk into all their risk management, portfolio rebalancing and option pricing models. Given its hand in the design of the credit crunch and the downfall of countless hedge funds, we've all seen how well that turned out! But still this idea persists...

Surely it's just common sense to know that risk isn't a number? You may be able to quantify it in vague terms, but you can't pin it down precisely. For the father of value investing,...