Giving away our personal power

Yesterday I played tennis in the evening and on the way home I stopped at a restaurant popular with young professionals for a beer and a salad.  Yes it's a weird food and beverage combination but my options were limited because I only had barely enough cash on me for a modest meal and a cab ride home later.  As I was seated at my table I noticed a rather attractive Asian girl sitting at her table in heated discussion with assumedly her boyfriend.   Her impassioned voice was loud enough to hear the content of the conversation without having to intentionally eavesdrop.  I discerned that they were disagreeing on the truth of the statement that one's figure can become toned purely on the merit of sustained weight resistance training without the accompaniment of a cardiovascular program.  I was struck by how incongruous their level of agitation was with the paltriness of the subject.  Each one expended so much energy into trying to convince the other of the truthfulness of their opinion, it never occurred to them that perhaps both could be right or maybe it really wasn't important if they disagreed and shared differing views on the subject.  Why are we so blinded by our need to have our beliefs be 'right'?  I read my book, finished my beer and salad and asked for the bill before the couple finally left.  I was impressed that for the entire duration there was not the slightest change in either one's stance on the subject that thoroughly dominated and upset their evening meal.