Three things cannot be retrieved:
The arrow once sped from the bow,
The word spoken in haste
The missed opportunity.
— Idries Shah, “Caravan of Dreams,” citing Ali the Lion, Caliph of Islam
Don’t make a threat that you’re not willing to make good on. And think over your words; only fools believe that people who take their time when speaking are slow.
As for opportunities, I don’t think it’s so dangerous to miss them. There are new ones every day.