FOMO
FOMO, fear of missing out, is the anxiety that a 's price is moving without you, and that waiting any longer means missing out on gains everyone else already appears to be getting. It pushes a decision to buy, or to keep holding past where the original justified it, based on what the crowd is doing rather than on an independent read of what the business is worth.
The danger sits less in the emotion itself than in the order it puts decisions in. A buy driven by FOMO starts from the price already moving and works backward to find a reason to justify it, the reverse of deciding a business deserves a position first and treating the entry price as a separate question. Deciding what would justify buying before the price starts moving, not after, is the most reliable way to keep that decision in your own hands instead of the crowd's.