ONE LUNCHTIME around 1960 a professor proposed a wager to a colleague. Flip a coin and call “heads” or “tails”. If you call right, you win $ 200. If you call wrong, you pay $ 100. This is a favourable bet for anyone who would take it. Even so, his colleague refused. He would feel the loss of $ 100 more than the gain of $ 200. But he would be happy, he said, to take 100 such bets.
The professor who offered the bet, Paul Samuelson, understood why it might be refused. A person’s capacity for risk could no more be changed than his nose, he once said. But he was irked by his colleague’s willingness to take 100 such wagers. Yes, the likelihood of losing money after that many tosses of the coin is vanishingly small. But someone who takes very many bets is also exposed to a small chance of far bigger loss. A lot of bets, reasoned Samuelson, were no safer than a single bet.
This lunchtime wager was of more than academic interest. It drew the battle lines in a debate on the merits of long-…
