It should be the aim of grand strategy to discover and pierce the Achilles' heel of the opposing government's power to make war. Strategy, in turn, should seek to penetrate a joint in the harness of the opposing forces. To apply one's strength where the opponent is strong weakens oneself disproportionately to the effect attained. To strike with strong effect, one must strike at weakness.
B. H. Liddell HartIn any problem where an opposing force exists and cannot be regulated, one must foresee and provide for alternative courses. Adaptability is the law which governs survival in war as in life ... To be practical, any plan must take account of the enemy's power to frustrate it; the best chance of overcoming such obstruction is to have a plan that can be easily varied to fit the circumstances met.
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 HartIf we clear the air of the fog of catchwords which surround the conduct of war, and grasp that in the human will lies the source and mainspring of all conflict, as of all other activities of man's life, it becomes clear that our object in war can only be attained by the subjugation of the opposing will. All acts, such as defeat in the field, propaganda, blockade, diplomacy, or attack on the centres of government and population, are seen to be but means to that end.
B. H. Liddell Hart