[04.02] Those skilled in warfare can make themselves invincible, but cannot necessarily cause the enemy to be vulnerable. Therefore it is said one may know how to win but cannot necessarily do it.
Guarantees in life are rare, especially when interests clash. And so it is not surprising to learn that guaranteeing victory in a combative situation isn't easy; it cannot be accomplished by securing only two variables: you and your opponent. According to Sun Tzu, it would also require a clear advantage in the environment you and your competition operate under. For example, the environment can represent the current legal, political, and social shifts that are in your favor. Otherwise, Sun Tzu advises, achieving success based on only knowing yourself and the competition would still depend on a little bit of luck, perhaps with odds not much better than a toss of coin:
[10.21] If I know the troops can attack, but do not know the enemy cannot attack, my victory is half.
[10.22] If I know the enemy can be attacked, but do not know the troops cannot attack, my victory is half.
[10.23] If I know the enemy can be attacked, and know the troops can attack, but do not know the ground in battle, my victory is half.
[10.24] Therefore, one who knows how to advance the army is limitless when taking action.
[10.25] Therefore I say, if you know the enemy and know yourself, the victory is not at risk. If you know the Heaven and you know the Ground, the victory is complete.
If there are relevant variables that affect a critical outcome for you, it would be a waste if you neglect to first gain advantages in them all before committing valuable and limited resources. Although you cannot control everything since not everything is controllable, you must be superior in those factors that are manageable or under your control.
By not trying to be fully prepared and ready, there are times when being halfway can leave you vulnerable:
[09.02] After crossing a river, you must stay far away from it. If the enemy crosses a river, do not meet him in the water. When half of his forces has crossed, it will then be advantageous to strike.
[04.06] Perceiving a victory when it is perceived by all is not the highest excellence.