FOMO is the fear of missing out: the pull to buy because everyone else seems to be winning. It is the most expensive feeling in trading, because it peaks at exactly the wrong time. The loudest hype almost always arrives at the top, not the bottom.
Hype moves in a cycle. Price runs, social feeds fill with certainty, latecomers pile in near the highs, and then the buyers run out. The move you are chasing already happened. By the time it feels safe and obvious, the easy gains are behind you.
When it feels euphoric and certain, you are usually late. The crowd is most confident right at the top.
Tip. Decide your entry and exit when the chart is quiet, then follow that plan. If the only reason to buy is that price is already flying, that is FOMO talking, not a plan.