
Most investors live by one ratio. That ratio that tells them all they want to know – or should one say all they want to hear? They open a screen, sort by it, and start picking from the bottom. It is the habit of a lifetime, and it is wrong more often than they realise. But add a single letter to the ratio and it changes which stocks look cheap, which look expensive, and which look like a trap. In a market that has gone nowhere for 20 months, getting that distinction right has rarely mattered more.