When others think you are angry, what do they see?  Non-verbals communicate more to others than your words do.  While you may think that you are being calm and reasonable, those around you may see a storm brewing. Your body language may well be triggering an alarm, sending them into fight, flight, or freeze mode.  In turn, you see their body language and get ready to fight, flight, or freeze yourself.  A conflict is ready to happen.  Mindfulness is being aware of your body language; connecting it to your triggers, emotions, and thoughts; and learning to allow those emotions without doing anything about it for a moment or two.  This is a great tool for avoiding conflict in relationships.