Čudovita zgodba Tima Harforda v Financial Timesu (ki dopolnjuje Nata Silverja v “The Signal and the Noise“) o tem, zakaj so eksperti izjemno slabi pri napovedovanju prihodnjih dogodkov. Zakaj? Ker svoje napovedi preveč bazirajo na privzetih modelskih ali miselnih konceptih, na sistematičnem, logičnem in nekritičnem razmišljanju, ker ne dopuščajo intuicije, ne spreminjajo mnenja, če se podatki spremenijo. Kot kažejo rezultati velikega eksperimenta Philipa Tetlocka “Good Judgment Project “, so bolj uspešni napovedovalci tisti, ki so manj samoprepričani in so sposobni spreminjati mnenje na podlagi novih informacij, ali na kratko: ki so pri svojem razmišljanju “aktivno odprte glave”.

Zgodba pa je odlično motivirana z različno uspešnostjo borznega investiranja med podjetnikom Rogerjem Babsonom, tedaj najboljšim ameriškim ekonomistom Irvingom Fisherjem in britanskim ekonomistom Johnom M. Keynesom. Babson je pravilno napovedal borzni zlom iz leta 1929 in obogatel. Fisher in Keynes sta se zmotila in izgubila premoženje. Toda Keynes je spremenil strategijo in nehal investirati na podlagi makroekonomskih napovedi, Fisher pa je vztrajal pri makro napovedih. Keynes je obogatel sebe in sklad King’s College univerze v Cambridgu, ki ga je upravljal, Irving pa je obubožal in umrl v revščini. Sedem desetletij kasneje je njegovi zgodbi “znanstveno” v propad zgrmel tudi sklad LTRM, ki je imel na krovu dva nobelovca s področja financ (glejte Kako smo znanstveno zavozili).

Yet Keynes is remembered today as a successful investor. This is not unreasonable. A study by David Chambers and Elroy Dimson, two financial economists, concluded that Keynes’s track record over a quarter century running the discretionary portfolio of King’s College Cambridge was excellent, outperforming market benchmarks by an average of six percentage points a year, an impressive margin.

This wasn’t because Keynes was a great economic forecaster. His original approach had been predicated on timing the business cycle, moving into and out of different investment classes depending on which way the economy itself was moving. This investment strategy was not a success, and after several years Keynes’s portfolio was almost 20 per cent behind the market as a whole.

The secret to Keynes’s eventual profits is that he changed his approach. He abandoned macroeconomic forecasting entirely. Instead, he sought out well-managed companies with strong dividend yields, and held on to them for the long term. This approach is now associated with Warren Buffett, who quotes Keynes’s investment maxims with approval. But the key insight is that the strategy does not require macroeconomic predictions. Keynes, the most influential macroeconomist in history, realised not only that such forecasts were beyond his skill but that they were unnecessary.

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As Roger Babson explained, not without sympathy, Fisher had failed because “he thinks the world is ruled by figures instead of feelings, or by theories instead of styles”.

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Fisher once declared that “the sagacious businessman is constantly forecasting”. But Keynes famously wrote of long-term forecasts, “About these matters there is no scientific basis on which to form any calculable probability whatever. We simply do not know.”

Vir: Tim Harford, Financial Times