> What Kent completely ignores here, as far a I can tell, is that there is significant value in finding out sooner what the needed features are.
But you're already know them, they come from your requirements and the design of the system that will fulfill those requirements. YAGNI is about creating something that is not part of the current requirements because you expect those requirements to change later. It's not about fleshing your current requirements and constraints (which mostly come with conversations with your stakeholders users/customer, your resources, and the engineering constraints and talents).
Creating prototypes only have value if you use them in your conversation with your stakeholders, building a project management model, or doing research for engineering purposes. Anything else is putting the cart before the horse.
But you're already know them, they come from your requirements and the design of the system that will fulfill those requirements. YAGNI is about creating something that is not part of the current requirements because you expect those requirements to change later. It's not about fleshing your current requirements and constraints (which mostly come with conversations with your stakeholders users/customer, your resources, and the engineering constraints and talents).
Creating prototypes only have value if you use them in your conversation with your stakeholders, building a project management model, or doing research for engineering purposes. Anything else is putting the cart before the horse.