When a customer cannot clearly define a major piece of functionality, attempting to lock down detailed requirements up front typically increases rework and delays value. The best approach is to use prototyping to make requirements tangible and accelerate learning. Building a prototype (B) enables rapid feedback, clarifies expectations, and reduces ambiguity by showing the customer working behavior rather than asking them to specify everything in words. This aligns with iterative delivery and progressive elaboration: deliver something small quickly, validate understanding, and refine. Assigning a BA to write detailed requirements (A) can help, but it still depends on the customer’s ability to articulate needs; it may create false certainty. Adding time/resources to estimating (C) is a delay strategy, not value delivery. Raising a risk (D) is appropriate to document uncertainty, but it does not solve the problem or create momentum. Prototyping supports early value, improves stakeholder alignment, and reduces failure risk by validating assumptions before full-scale build.

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