Newton's third law of physics, about the balance between action and reaction, plays out in digital medium. The very notion of interaction is that a user undertakes an action expecting to evoke a reaction (if I click a link, a page will load), though this is not so strong as a "law" as there are instances in which reaction simply does not occur (I click a graphic based on my expectation that something will happen, but nothing actually does).
And so, the author revises Newton's law: "For every action, there is an opportunity for an intelligent reaction." (EN: fro ma UX perspective, this might be better phrased that "there is the expectation of a reaction" - and success in design is ensuring that the expectation is fulfilled.)
The notion of action-reaction is the focus of the present book, and is also one of the most important issues facing marketing (and business in general) today. But it isn't so much a "how to" approach for measuring analytics, as it is geared to explaining "why to" consider reactions, and "what to" do with the information you find.
On the Internet, users generate a vast amount of data that can be observed, collected, and analyzed - but unless you ask the right questions, the data yields little meaning, and unless you take the right actions, the data produces no benefit. The present state of Web analytics I such that companies overlook significant data, fail to analyze it appropriately, and fail to take action - which reduces it to meaningless activity.
The present book proposes to address this problem, primarily from the perspective of marketing, which focuses on technology (specifically, your Web site) as a channel for interacting with customers that can be measured, monitored, and improved to result in more profitable and long-term relationships (which themselves are a sequence of related interactions) with customers.