A quote from Tony Blair’s memoir
It is amazing that people constantly miss the importance of the fact that any threat made in international affairs must be credible. The absence of credibility actually increases the likelihood of confrontation. The recipient of the threat doesn’t believe it, so he carries on; then the very choice you are trying to avoid-go to war or not-is the one you are forced to make. I saw this time after time after time. We are about to witness the same wretched business over Iran. Back up the demand with a credible threat, and the demand has a good prospect of being satisfied. If you seem unsure about how far you will go to enforce a demand, confrontation becomes almost inevitable.