End-user testing is critical in product development as it ensures the final product meets the needs and expectations of its intended users. This phase involves observing real users as they interact with the product to identify any usability issues, gather feedback, and assess overall satisfaction. By involving end-users, developers can uncover potential design flaws and functional shortfalls that may not be apparent through internal testing alone. Ultimately, this process not only improves product quality but also enhances user adoption and engagement once the product is launched.