Even the finest sword plunged into salt water will eventually rust.

More from Sun Tzu

• All warfare is based on deception.
• The art of war is of vital importance to the State. It is a matter of life and death, a road either to safety or to ruin.
• Attack him where he is unprepared, appear where you are not expected.
• Now the general who wins a battle makes many calculations in his temple ere the battle is fought. The general who loses a battle makes but few calculations beforehand.
• There is no instance of a country having benefited from prolonged warfare.
• To fight and conquer in all your battles is not supreme excellence; supreme excellence consists in breaking the enemy's resistance without fighting.