Force and volume are not the same as clarity. A hard message delivered quietly is harder to dismiss, because there is nothing for the other person to react to except the content. Raising your voice gives them an easy exit, since now the conversation is about how you said it. Calm is not weakness, it is refusing to hand over the subject.

Say the difficult sentence this week in your normal voice, slowly, and then stop. Let the pause after it do the work you were going to do with volume.