The core concept in this paragraph is really a basic concept in outsourcing - don't outsource your business's core product, or you will be at a disadvantage when competition comes.
Notice, he doesn't say that you cannot use these extra forces in attacks. All he is saying is that if they are guarding your sleep, you are probably screwed. Similarly, if your core business is being a technology organization, if you chose to outsource that core tech, you are likely screwing yourself. Now, should outsource as much as possible the non-core aspects, either by buying software/services or by hiring consultants, while you let your core team focus on what they do best.
Of course, it's all easier said than done, and the line between core and non-core is often blurred.
Notice, he doesn't say that you cannot use these extra forces in attacks. All he is saying is that if they are guarding your sleep, you are probably screwed. Similarly, if your core business is being a technology organization, if you chose to outsource that core tech, you are likely screwing yourself. Now, should outsource as much as possible the non-core aspects, either by buying software/services or by hiring consultants, while you let your core team focus on what they do best.
Of course, it's all easier said than done, and the line between core and non-core is often blurred.