Mean What You Say
If you don’t, people will cease to take you seriously.
It doesn’t take much experience on your part to realize that people make promises and commitments that they can’t keep either because they are not competent enough to do so. Or, it may be that they don’t follow through on their commitments because that has become the norm for them. They’ve become used to lying to themselves and to others.
In a conventional organization, commitments are often not treated seriously. It’s easy for someone to say to your face that they will do something. But if doing it gets to be too difficult or onerous for them, they may resort to a secondary kind of competence – their growing competence to explain why it didn’t happen. It was never their fault.
Work on yourself first. If you invariably say what you mean – what strategically needs saying – those who report to you will get the message that is how you want things done.
If they don’t get the message after that, make it necessary for them to say what they mean today (with the appropriate level of consequences for them if they don’t).
If that doesn’t work, you will either have to pay the price of replacing them. Or pay the price of their fake commitments from then on.