The student of the Way of strategy has to know different aspects: Ground, Water, Fire, Wind, and Void.
Here is what the books say:

"Stand up, climb the stairs, and be prepared for your quest. Know the smallest things and the biggest things,
the shallowest things and the deepest things, as if there were a straight road mapped out on the ground. 

Then the spirit becomes like water. Water adopts the shape of its receptacle, it is sometimes a trickle and
sometimes a wild sea. The strategist makes small things into big things, like building a great Buddha from one
foot model. The principle of Water is having one thing, to know ten thousand things. 

Next is the spirit of fire which is fierce, whether the fire be small or big; and so it is with battles. It is difficult for
large numbers of men to change position, so their movements can be easily predicted. An individual can easily change
his mind, so his movements are difficult to predict. Master the essence of the strategy and be as unpredictable
as fire. Be the tiny match that will make the fire endlessly growing. 

Never forget that Wind is Tradition. It is difficult to know yourself if you do not know others. To all Ways
there are side-tracks. If you are following the true Way and diverge a little, this will later become a large divergence,
and you may think you are still obeying a good way. The tradition is only a guide and cannot do anything for you,
because it is your quest. But you shall realize that you have been in the tradition all this time. 

______________________ 

Finally, the spirit of Void has no beginning and no end. Void is nothingness, it is not included in
man's knowledge. By knowing things that exist, you can know that which does not exist. That is
the void. Darkness does not exist, only light does. 

People in this world look at things mistakenly, and think that what they do not understand must be the void.
This is not the true void. It is bewilderment. 

With your spirit settled, accumulate practice day by day, and hour by hour. Polish the twofold spirit heart and
mind, and sharpen the twofold gaze perception and sight. When your spirit is not in the least clouded, when the clouds
of bewilderment clear away, there is the true void. 

Until you realize the true Way, whether in Buddhism or in common sense, you may think that things are correct and
in order. However, if we look at things objectively, from the viewpoint of laws of the world, we see various doctrines departing
from the true Way. Enact strategy broadly, correctly and openly. Know well the true spirit as the Way,
and with forthrightness as the foundation.