He who excels as a fighter is never aroused in anger.

I have already discussed the true nature of combat, its potentially fatal risks, and the potential need for massive and total retaliation in the face of a truly lethal threat.
The excellent fighter realises the true nature of combat. Realising the risks involved and the potential costs - pain, injury, criminal charges, remorse - he seeks to avoid it wherever possible. He will try to resolve potential conflicts using his brain rather than his fists, to use psychology on an opponent rather than smashing his face in. To do so requires awareness, confidence, and self control.
Anger is the enemy of control. Anger causes overreaction, resulting either in rushing in, creating openings which can be exploited by a calmer, thinking fighter, taking on an opponent or opponents due to wounded pride that in a more lucid moment we know we should run from, or in losing control of ourselves and causing unjustified pain or injury, resulting in guilt and remorse at best, criminal charges or violent retribution at worst. Strategy and tactics demand the ability to analyse the situation rapidly, which is impossible when we are burning with anger, out of control.
While a skilled fighter generates and recognises emotion, adrenalin, and the fight or flight reaction within himself and allows them to carry him through, the point is to consciously channel the emotions to achieve victory, not to allow oneself to become consumed by them.