This proverb is from Sun Tzu's (Sunzi's) Art of War.

It means that if you know and understand the enemy, you also know yourself. Four secondary characters come after this in the Art of War (not included here) which suggests you cannot lose a battle when you follow this philosophy.

In a very literal and somewhat-boring way, this can also be translated as “Estimate correctly one's strength as well as that of one's opponent.”

敵を知り己を知る is the Japanese version of “know your enemy, know yourself.”

There is a longer version of this proverb that adds, “...and you can win 100 battles.”

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.

正勝吾勝 is a proverb that is often translated as “True victory is victory over oneself.”

However, literally, Kanji by Kanji, means “True victory [is] my/self victory.”

My Japanese friends rate this very highly for a wall scroll.

See Also:  Know Thy Enemy Know Thyself

These are the “Five Reflections” of Vice Admiral Hajime Matsushita of the Japanese Imperial Navy.

These days, the Five Reflections are recited or contemplated daily by Japan Maritime Self-Defense Force recruits in training. This long proverb is popularly translated into English this way:

Hast thou not gone against sincerity?
Hast thou not felt ashamed of thy words and deeds?
Hast thou not lacked vigor?
Hast thou not exerted all possible efforts?
Hast thou not become slothful?

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.