[SoCal Pubbie]

In Europe of the Middle Ages, laying siege was THE way of conducting warfare. Pitched battles on open fields was too risky- you might lose your whole army in a single day!

Conducting a siege usually meant just surrounding a city and starving it out. Unless a relief force was on the way, there was no need to do much more than fling a few dead horses and diseased corpses over the wall with the trebuchet your engineers just built.

[Eric in the Ozarks]

Sun Tzu's point was it was better to use trickery and stealth and it was always best to hit the enemy when it is not expecting an attack (hit em where they ain't).
Modern business schools teach Sun Tzu to show it is better to spend resources where your advantage cannot be duplicated.