The project manager needs to understand what makes the outputs acceptable to the users.

In the 'planning' technique of PRINCE2, understanding what makes the outputs acceptable to the users occurs during the step of "Defining and Analyzing the Products." This step involves detailed discussions about product requirements and specifications to ensure clarity on what the project must deliver for it to be accepted by the users. It sets out the criteria that the products must meet to satisfy the user's needs and expectations.References: (PRINCE2® 7 Foundation Handbook, AXELOS)