"Further, a defensive policy involves the loss of the initiative, with all the consequent disadvantages to the defender"

This quote by Douglas Haig is referring to the downsides of a protective policy in warfare. He is recommending that when a protective policy is embraced, the initiative is lost, indicating that the defender is no longer in control of the situation. This can be unfavorable as the protector is no longer able to determine the regards to the battle, and rather must respond to the actions of the assailant. This can cause an absence of control over the result of the battle, as the defender is not able to take the initiative and make choices that will cause a favourable result. Moreover, the defender may be at a drawback in terms of resources and manpower, as they are unable to plan ahead and get ready for the battle in the very same way as the aggressor. Ultimately, Haig is recommending that a defensive policy can be unfavorable, as it can lead to a lack of control and effort, and can put the protector at a drawback in terms of resources.