“The courage of a soldier is heightened by his knowledge of his profession,”
Scientia enim rei bellicae dimicandi nutrit audaciam: nemo facere metuit quod se bene didicisse confidit.
Publius Flavius Vegetius Renatus book De re militari
De Re Militari (also Epitoma Rei Militaris), Book I, "The Selection and Training of New Levies"
Context: The courage of a soldier is heightened by his knowledge of his profession, and he only wants an opportunity to execute what he is convinced he has been perfectly taught. (Book 1)