Legendary 19th century financier JP Morgan said, “A man generally has two good reasons for doing a thing—one that sounds good, and a real one.” Pundits cite loads of seemingly smart reasons you should dismiss global stocks’ rally since March. But their real reason? Admitting the upturn is real also admits they were wrong. Tough for most of us! So instead, they grasp for anything supporting their prior negativity. Behavioral psychologists see this as a subset of “confirmation bias.” It drives the “Pessimism of Disbelief”—the foundation of every new bull market, as I highlighted in May. Those falling prey it to suffer a costly but simple behavioral error.