There is an ancient Chinese maxim which states that “the best soldiers are not warlike, the best fighters do not lose their temper” which remains a profoundly accurate observation that holds merit on a variety of levels.
Lao Tzu, who coined the phrase, was advocating for a subtle approach to conflict, in which he believed the best way to overcome ones adversaries was without bloodshed. The Chinese approach to warfare has oft been to minimise loss and achieve victory without recourse to the decisive battle so favoured by the West. In this aspect alone the Classical Chinese virtue may be observed in the saying, bestowing the thoughtful soldier with qualities admirable to his society.
In addition to the societal approach to war inherent in the maxim, however, further meaning may be drawn even to the individual level. From commander to frontline soldier it can be observed that violent aggression is a detrimental trait in soldiers; the ultimate fate of many warrior societies upon their encounters with developed armies should provide apr evidence of this. Much modern training in the West (I must confess I have little knowledge of training outside the Western world) is designed to weed out violent recruits and limit aggression to the times it is most required.
The aggressive soldier is detrimental to their unit, as they will think less clearly in times of stress and may lash out impulsively rather than follow orders. The desire to attack and do harm is a personal one and deeply selfish, and will threaten to undermine the cooperation necessary for success on the battlefield.
At all levels of military thinking violence should not be the default response; the use of force should be measured and rational in order to achieve the ends without unnecessary loss of life. This is not to suggest that all military goals can be achieved without violence, but that its application should only be realised if it is appropriate. To this end the best soldiers are those to whom the use of force is a necessary evil, rather than a preferable choice. The best military leader is one who is able to suffer losses, cause harm, and use any means at their disposal to fight a war, but to also be unwilling to start one.