Identifying Cognitive Errors in Investment Behavior

John, an experienced investor, has recently encountered significant losses due to a poorly timed investment in a high-growth tech stock. Despite recognizing the stock's poor performance, he continues to hold the stock, convinced that it will eventually return to its previous highs. He dismisses analysts' opinions and media reports indicating worsening fundamentals. This behavior is representative of a specific cognitive error that can impact investment decisions. Which cognitive error is John exhibiting?