Martial artists are disciplined and structured fighters but, in a situation, emotions can inhibit their performance. This is because emotions and fighting don’t mix very well. We've heard it many times over ‘keeping a cool head’ is the best advice in a situation. This is demonstrated by well trained police officers, doormen etc who keep their cool and will do a much better job in comparison with the ‘ordinary guy’.
Police officers, and the like, generally are able to keep their emotions under control because what they do is not personal. They get involved in a situation because it's their job to do so unllike the ordinary guy who may get involved in a heated situation with emotions flaring up. The more personal, the more emotional, the more difficult to perform.
How does one keep a cool head? Ask the the experts; these are the people you want to talk to or learn from. Keeping calm is not only better for performance but when the Cops turn up, the first thing they do, is will want to talk to the person who is most composed when trying to figure out what has happened or who is the culprit. If they don't like you, you are already behind the '8' ball so you need to remain calm.
Relaxing is not so easy for the ordinary guy because they are not acclimatised to confrontations but just be aware the less emotional you are, the less likely you are to say something stupid and do the wrong thing.
PS: Happy Birthday to Soke Richard Norton