Drawing on experience from a variety of real world systems – nuclear power plants, oil rigs, aircraft navigation systems – Tim Harford (2011) illustrates how complex control of a complex environment has often been calamitous. The general message here is that the more complex the environment, the greater the perils of complex control. The optimal response to a complex environment is often not a fully state-contingent rule. Rather, it is to simplify and streamline (Gigerenzer (2010)). In complex environments, decision rules based on one, or a few, good reasons can trump sophisticated alternatives. Less may be more. In Isaiah Berlin’s famous essay “The Hedgehog and the Fox” (Berlin (1953)), the fox knew many things, the hedgehog one big thing. Philosophers continue to debate their relative merits. But sports fans, doctors and detectives have made their choice. They think the hedgehog has the upper paw. Selective unclogging of the cognitive inbox can make for better decisions. (c)  Weighting may be in vain  John von Neumann and Oskar Morgenstern established that optimal decision-making involved probabilistically-weighting all possible future outcomes (von Neumann and Morgenstern (1944)). Multiple regression techniques are the statistical analogue of von Neumann-Morgenstern optimisation, with behaviour inferred by probabilistically-weighting explanatory factors. 3  Gigerenzer and Kurzenhäuser (2005). 4  Snook et al (2005). 5  DeMiguel et al (2007). 6  Wübben and von Wangenheim (2008)). 4  BIS central bankers’ speeches  In an uncertain environment, where statistical probabilities are unknown, however, these approaches to decision-making may no longer be suitable.

Were these proposals to become mired in detail, they risk sinking, like the Tower of Basel, into the swamp. This is not because these proposals go too far but because they may not go far enough. These reform efforts have too many commas, semi-colons and sub-clauses. They would benefit from a few more full stops. That logic suggests cleaner solutions than are currently being implemented, if not than are currently being contemplated. Strict size limits and forced separation of commercial and investment banking are two frequently cited such radical options (Haldane (2010), Fisher (2011), Johnson and Kwak (2010)). The debate on them has waxed and waned on both sides of the Atlantic. A stalemate has been reached. Having risen to a peak of almost three in 1928, the largest US banks’ price-to-book ratios had by 1931 plummeted to below one. They remained close to these levels for several years afterwards (Chart 20). This discount implied that investors in the bank could improve their wealth by selling-off the banks’ assets separately. Investor pressures to separate began to mount. In response, a number of banks began selling off their equity brokerage affiliates, including the two largest banks, Chase National Bank and National City Bank in 1933. A number of banks delisted their shares. This response, led by the market, paved the way for the passage of Glass-Steagall in 1933. As Fuller (2009) puts it: “Divorce made a virtue of necessity and cursed and condemned bankers jumped at the opportunity to demonstrate their virtue”.