Defense requires less troops then offence

In military strategy it is common thought that it requires 3-5 times more troops to attack then to defend.  In its most simple axiom- defence requires less offense.  Why?  Someone who  defending feels a greater sence of purpose.  They may feel more is at stake.  This is true in business as well.  Have a clearly defined purpose for your business that you know is of value to your customer and you are far more likely to effectively defend  (promote, advertise it).