At the apex of the inverted funnel is the customer theory. One must understand the customer theory before they can map the yes-path. The customer theory represents the sum of what the organization knows about its customers (and so what it may discern about its ideal prospects). Sustainable Competitive Advantage (a Michael Porter term) is derived from, I think, a robust customers theory.
Too often, marketers are focused on results instead of reasons. We need to move deeper than “how much”, into “why so”, to answer an even more important question: What does this tell me about my customer/prospect? And so the goal of an optimization test transcends the notion of a lift and asks for learning. With sufficient insights we can obtain the ultimate lift. The more you know about the customer, the easier it is to predict their behavior. The easier it is to predict their behavior, the more you know about your value proposition.