22. Dispersion allows near unlimited damage absorption.

When forces are concentrated, they may be encircled and systematically eliminated.  When forces are dispursed, they must be individually hunted down and destroyed.  While the aggressor is able to destroy anything encountered, the defender is able to replace and reposition anything that is destroyed.  In this way, the defender only loses assets in a short term timeline.  Further, the defender may constantly harass aggressive forces making their assault excessively costly.  So long as the offensive ability of the assaulting forces is not increased, the defender may retreat and replace his assets indefinitely.

21. Redundancy is survivability.

When faced with any scenario, there will always be random elements that can not be forseen in any capacity and mitigating the risk they impose upon your efforts may be impossible to entirely manage for that reason.  The statistical probabilty that any one method will succeed or any one item will survive is enough to consider gambling with the odds.  The purpose of gambling in this fashion is not to risk success, but to chance which contingency will succeed.  Always assume that your opponent will be able to destroy your base, so build multiple bases around the world.  Always assume that your opponent will be able to defeat your assault, so plot multiple methods of simultaneous attack.

If seige bots are sure to succeed, then also send heavy tanks from the opposite direction in case of unforseen disaster.  If gunships are sure to succeed, then also send bombers in case of unexpected anti-air capabilities.  If shields are sure to absorb all of the damage, then walls can only help to support that effect.

At worst, you will acheive an innefficient victory.  At best, you will narrowly succeed where you should have failed otherwise.