Play card games.
Mostly you don't say what you have. If anything, you try to make the opponent think you have more than you do have.
Often you bluff. "Under no circumstances will we use military force" immediately tells the other side that whatever we do is going to involve jaw-jaw and perhaps some money. And the jaw-jaw might wind up being the more painful to endure.
I mean, could you seriously imagine being Taiwan and have the US president say, "We will not defend Taiwan using anything but diplomacy, and if hostilities are threatened we will move our troops and military assets to a safe distance at once until we can ensure our soldiers' safety." I'd expect hostilities to be threatened the next day.
It's like being dealt a hand in poker and saying, "These cards suck"--and have everybody else at the table know that you really mean that you have nothing. It's like sending in the Golden State Warriors with 2/3 of the team wearing casts. On their arms.
It helps if the leader in charge of the military is unpredictable. The more unpredictable the threat, the more likely it is to be effective.