More than 70 years ago, two Columbia professors named Benjamin Graham and David L. Dodd came up with a simple investing idea that remains more influential than perhaps any other. In the wake of the stock market crash in 1929, they urged investors to focus on hard facts — like a company’s past earnings and the value of its assets — rather than trying to guess what the future would bring. A company with strong profits and a relatively low stock price was probably undervalued, they said.Their...