Thucydides (c. 460-400 BCE)
“If a stout heart is lacking, all the skill in the world will not avail in the face of peril. Fear drives out all memory of previous instruction, and without the will to resist, skill is useless.”
- History of the Peloponnesian War (Book II) by Thucydides, translated by Rex Warner (Penguin Classics, 1972). The quote comes from a speech that Thucydides wrote while in the character of Diodotus.