知己知彼，（百战不殆）- Only knowing yourself, as well as your opponents, (you will never lose a battle).

If knowing yourself, as well as your opponents, you will never lose a battle, This emphasizes on the importance of knowledge and preparation before you do anything. You have to know your stuff, know where you are in the field, know where others are in the field, so that you can work consciously to improve yourself, to jump to the front.