I've been carrying Sun Tzu and reading it almost daily since I first picked it up in 1950. After some good OJT, the knowledge in these books and others will allow you to lead well, fight smart, and take care of your warriors. A good knowledge of military history, like attending Airborne, Ranger, and Special Forces courses, is a confidence builder. In small-unit leaders, confidence, like fear, is contagious. Troopers can feel it, see it, smell it, and it will rub off on soldiers from a platoon to a division as quickly as a good rumor rumbles out of the latrine.
Confidence produces courage.
Most leaders or warriors are not born with a double basic load of guts. Most leaders and warriors are as scared as the next guy in their first or 100th firefight, but if they are confident that they are tactically proficient and their unit is squared away and motivated by a strong sense of duty to accomplish the mission, the courage that is needed to do what many will view as impossible will be there. And no one will know who is scared out of their brain. Besides being one hell of a job, leading men into battle is the ultimate responsibility. Leaders carry the scars of those decisions for the rest of their lives.