Robert H. Scales Jr. said this quote

“ As a ground-combat force approaches the deadly zone and moves within range of the enemy’s rifles, mortars, and machine guns, the dynamics of war become more art than science. Intangibles such as training, confidence, leadership, and cohesion provide more secure mantle of protection than the possession of superior equipment.”There is as much folklore as science in the accounts of maneuver units that do exceptionally well in close combat. Empirical and anecdotal evidence gathered from combat studies of the Second World War, Korea, and Vietnam has shown conclusively that elite maneuver units, carefully selected and trained, not only perform better in combat but do so with many fewer casualties from all sources of combat incapacitation (for example, from disease and combat fatigue). Such units fight so effectively because they are composed of soldiers of exceptionally quality – better trained and better led as well as coalesced through long-term association that builds familiarity and mutual trust. The difference between carefully trained and led units and those of lesser quality is dramatic. ”