If we always knew the enemy's intentions beforehand, we should always, even with inferior forces, be superior to him.
While the wish to achieve surprise is common and, indeed, indispensable, and while it is true that it will never be completely ineffective, it is equally true that by its very nature surprise can rarely be outstandingly successful. It would be a mistake, therefore, to regard surprise as a key element of success in war. The principle is highly attractive in theory, but in practice it is often held up by the friction of the whole machine.
Basically, surprise is a tactical device, simply because in tactics, time and space are limited in scale. Therefore in strategy surprise becomes more feasible the closer it occurs to the tactical realm, and more difficult, the more it approaches the higher levels of policy.
Preparations for war usually take months. Concentrating troops at their main assembly points generally requires the installation of supply dumps and depots, as well as considerable troop movements, whose purpose can be guessed soon enough.
It is very rare therefore that one state surprises another, either by an attack or by preparations for war. ... Cases in which such surprises lead to major results are very rare. From this we may conclude how considerable are the inherent difficulties.
The enemy force can never assemble and advance so secretly that the defender's first news of it would come from his outposts. If that were to happen, one could only feel very sorry for him.
We say this in order to exclude certain vague notions about sudden assaults and surprise attacks which are commonly thought of as bountiful sources of victory. They will only be that under exceptional circumstances.
[Tu yu] They [the experts] make it impossible for an enemy to know where to prepare. They release the attack like a lightning bolt from above the nine-Iayered heavens.
Appear at places to which he must hasten, move swiftly where he does not expect you.
[Chang yu] Take him unaware by surprise attacks where he is unprepared. Hit him suddenly with shock troops.