Confirmation Bias

Confirmation bias is the tendency to seek out, favor, and remember information that confirms an existing belief while ignoring or discounting information that contradicts it. In investing, this often shows up as only reading bullish analysis on a stock you already own and dismissing bearish arguments without giving them equal weight.

The bias is especially dangerous after a position has already lost money, since an investor emotionally invested in being right becomes more likely to selectively seek reasons to hold on rather than objectively reassess the original thesis.