Collingwood on Self-Knowledge

R. H. Collingwood approaches knowledge as if it were one of the martial arts:

Without some knowledge of himself [man’s] knowledge of other things is imperfect; for to know something without knowing that one knows it is to only a half-knowing, and to know that one knows is to know oneself. Self-knowledge is desirable and important to man, not only for its own sake, but as a condition without which no other knowledge can be critically justified and securely based. Self-knowledge, here, means not knowledge of man’s bodily nature, his anatomy and physiology; nor even a knowledge of his mind, so far as that consists of feeling, sensation, and emotion; but as knowledge of his knowing faculties, his thought or understanding or reason. How is such knowledge to be attained? It seems an easy matter until we think seriously about it; and then it seems so difficult that we are tempted to think it impossible.

R. G. Collingwood, The Idea of History 205 (Oxford UP paperback ed. 1961)