Probable vs. Possible

Good advice from Jim O’Shaughnessy:

Investors should make decisions using the long-term base rates a strategy exhibits—in other words, they should concentrate on what is probable rather than what is possible. If you organized your life around things that might possibly happen to you, you’d probably never leave your house, and when you did, it would only be to buy a lottery ticket. Consider, on a drive to the supermarket, it is highly probable that you will get there, buy your groceries and get back home to unpack them without incident. But what’s possible? Almost anything—it’s possible a plane flying overhead could lose an engine falling directly on your car and instantly killing you. It’s possible another car runs a red light and kills you on impact. It’s possible that It’s possible that you get carjacked and your assailant kills you in the process. You get the point—anything is possible buy highly improbable. It’s only when you think in terms of probability that you will get in your car and go, yet few investors do so when making investment decisions. Our brains create cause and effect narratives after something has occurred that seem to make sense, however improbable the event. Witness anyone who invested in the stocks with the highest sales gains after a great short-term run.

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