A PhD in finance corners you in a meeting and asks what I think of the efficient frontier and mean-variance optimization. Fair question. My honest answer is that the theory has earned its keep. It gave the industry a common language and a useful starting point. The problem starts when people begin treating the model…

I’m writing this at the train station, waiting for a train. Seemed like the right place for it where everyone around me looks faintly annoyed in a world where trains, on the whole, run better than they ever have in human history. Well, I told some friends this at dinner recently. They did not believe…