For almost seven decades, the 60/40 portfolio has been the comforting failsafe for investors. Stocks up, bonds down, and vice versa. The tumult gripping Wall Street is proving to be that wisdom’s biggest test yet.

The strategy is simple. Investing 60 per cent of a portfolio in stocks and 40 per cent in bonds ensured good returns as the economy grows, pushing up equities as profits grow, and as it slows, when bonds go up in price.