Sometimes business requirements truly change because of some change external to the project; then again there are times where a business user simply can’t make up his/her mind on what is needed creating frustration with team members.
Question to ask: What is the degree of confidence on each requirement? If not 100%, what will it take to get it to 100%?
The project sponsor needs to own decision-making where the project team needs direction. Failing to do so can stall the project or force the project team to make the decision themselves in spirit of keeping the project moving forward.
Question to ask: Is the sponsor driving a list of key decisions needing to be made with clear consequence if a decision is not made by a specific date?