When we're confident and relaxed, we can deal with aggression or confrontation easier than if we're inclined ourselves to part someone's hair with some well-chosen words. We all know how easy it is to not only get drawn into an argument or dispute but to fuel it as well. We sometimes think 'if this person wants confrontation, then I'll make sure they get it'. You can avoid a tense spiral from happening if you wish to. All you have to do is keep your voice at conversational level!