The effect to be sought is the dislocation of the opponent's mind and dispositions - such an effect is the true gauge of an indirect approach.
B. H. Liddell HartWhile hitting one must guard ... In order to hit with effect, the enemy must be taken off his guard.
B. H. Liddell HartThe unexpected cannot guarantee success, but it guarantees the best chance of success.
B. H. Liddell HartThe art of the indirect approach can only be mastered, and its full scope appreciated, by study of and reflection upon the whole history of war. But we can at least crystallize the lessons into two simple maxims- one negative, the other positive. The first is that, in face of the overwhelming evidence of history, no general is justified in launching his troops to a direct attack upon an enemy firmly in position. The second, that instead of seeking to upset the enemy's equilibrium by one's attack, it must be upset before a real attack is, or can be successfully launched
B. H. Liddell Hart