This paper contrasts two approaches to startups: the lean startup and the theory-based view. The lean startup emphasizes rapid customer feedback and bounded rationality, while the theory-based view focuses on generative rationality and contrarian beliefs. The lean startup's emphasis on information asymmetry and bounded rationality is critiqued for its limitations, particularly in handling heterogeneous customer feedback and novel product offerings. In contrast, the theory-based view sees entrepreneurs as generative agents who use theories to direct their attention and learning, emphasizing the importance of contrarian beliefs and problem-solving. The paper introduces the Value Lab, a practical framework based on the theory-based view, which guides entrepreneurs through articulating contrarian beliefs, formulating problems, and developing a causal logic for value creation. This framework aims to help startups create unique value by focusing on theory-specific search and problem-solving, rather than relying solely on customer feedback.This paper contrasts two approaches to startups: the lean startup and the theory-based view. The lean startup emphasizes rapid customer feedback and bounded rationality, while the theory-based view focuses on generative rationality and contrarian beliefs. The lean startup's emphasis on information asymmetry and bounded rationality is critiqued for its limitations, particularly in handling heterogeneous customer feedback and novel product offerings. In contrast, the theory-based view sees entrepreneurs as generative agents who use theories to direct their attention and learning, emphasizing the importance of contrarian beliefs and problem-solving. The paper introduces the Value Lab, a practical framework based on the theory-based view, which guides entrepreneurs through articulating contrarian beliefs, formulating problems, and developing a causal logic for value creation. This framework aims to help startups create unique value by focusing on theory-specific search and problem-solving, rather than relying solely on customer feedback.