Anger and Ego
From all the countless discussions that i have had in my life, there is one conclusion that distinctly emerges: a heated argument does not convince anyone, no matter how rational or logical it may be. There is something about anger that shuts off the rational part of your mind; prevents you from accepting what is right, even when the logical part of you knows that it is right. A person only accepts an argument, is only willing to change his mind, when he is cool and calm. And this state may be difficult to achieve, particularly if the issue becomes a matter of ego, and accepting an argument is seen as a way of losing one's pride. There are very few people who can rise above their vanity to accept an opposing argument or admit that they are wrong.