Ann: Becoming a substantial holder from MUFG, page-52

People lose their minds at a contrarian view because it's diametrically opposed to their beliefs. The closer the belief is to the sense or understanding of 'self' the harder the prefrontal cortex works to protect against threats. This is why we stubbornly hold onto losing positions or even double down into a receding stock - even though there is empirical evidence that shows statistically, on above average results, that this just compounds your losses.

This to me is the underlying reason why so many lose. It's easily exploited for one, and also very difficult to overcome (let alone recognize).