The human mind works at its best when the surrounding environment is calm and settled. Likewise, it works at its best when the thinker's temperament is calm. When the human mind is beset with external or internal commotion, its powers become weak and it more easily falls prey to rashness and reckless passion.
It is a strategy of debate to get one's opponent angry, since once the opponent loses his or her composure his or her defeat is almost imminent, especially if one is able to keep one's cool and a smile on one's face.
The Prophet (peace be upon him) warns us that: "Anger is a burning ember in the human heart that is stoked up." [Musnad Ahmad]
The Prophet's conducts should remind us that just because we know we are in the right, this gives us no excuse to get angry. Indeed, if we are upon the truth, this should give us all the more reason to remain calm. Anger merely confuses things and makes it more difficult for us to think clearly and communicate our thoughts to others.
We should remember the Prophet's words: "The strong person is not the one who can throw his opponent. The strong person is the one who can keep control when angry." [Bukhari]
"Calm" - Salman al-Oadah