There is a depth of meaning in the original Chinese that cannot be captured in translation. Each Chinese character of the key concepts in Sun Tzu's work requires an essay to explain. Put a number of those characters together, and you get complex formulas. Because of the depth of meaning in each character, every line in The Art of War has a wealth of useful applications, just like each value in a mathematical formula has a wealth of implications.

Look at these two lines:

Know the enemy and know yourself.
Your victory will be painless.
Sun Tzu’s The Art of War 10:5.15-16

One simplified meaning of that stanza is as follows:

If you have highly accurate information (to know) about your and your opponents' relative strengths and weaknesses (the enemy and yourself), you can only meet that enemy either when you are both ready to join together as allies or when you overmatch that enemy to such an obvious degree (victory) that he will surrender without a fight (painless).

However, another simplified but accurate interpretation of this line is also possible:

If you have avoided self-deception and accurately interpreted the motivations (to know) behind your opponent's moves (your enemy), you can find a place (yourself) where you will invest much less in winning a dominant position (victory) than the position is worth in terms of its tangible rewards (painless).

Other different interpretations would bring to light the various other aspects of the deeper meaning of these terms. All these interpretations are useful in terms of applying the methods of Sun Tzu's strategy to a specific situation.