What it means
No setup, no trade. A missed trade costs nothing; a chased one usually costs.
In practice
FOMO appears when price is moving fast without you. The entry it produces is late and far from any sensible stop, so the position is either oversized or carries a stop that normal movement will hit.
Traders manage it with rules made in calm moments: only planned setups are traded, and a move that was missed is noted and left alone. Another setup always comes.
What to watch for
Social media makes it worse by showing other people's wins and never their losses. The strongest urge to chase tends to come near the end of a move, when the late buyers become the fuel for the reversal.