Choose on uncertainty and the cost of change. If requirements will move and iterating is cheap, run iteratively. If scope is fixed by a regulator or a contract, or a late change costs a fortune (hardware, physical build, a migration cutover), phased planning fits better. Most real projects are hybrid: an iterative build inside fixed external milestones, and that is the version worth describing.
Why interviewers ask this
Interviewers use this to filter out methodology zealots. They want a decision made on project characteristics rather than fashion, and they want to hear that you have run the hybrid version, because almost every real organization has fixed external commitments wrapped around iterative delivery. Naming the worst of both worlds, iterative delivery against a detailed scope signed off months earlier, shows you have lived through it.
How to structure your answer
- Decide on uncertainty and the cost of a late change.
- Give a concrete case for each approach.
- Describe the hybrid you have actually run.
- Name the failed combination you avoid.
Example answer
I choose on how much the requirements are going to move and how expensive a late change is. If we genuinely do not know what good looks like until people use it, iterating is the only honest approach. If the scope is set by a regulator or a fixed price contract, or the cost of changing your mind late is enormous, like hardware or a data center cutover, phased planning fits better. In practice most of what I have run is hybrid. On a platform migration we had immovable external milestones, a regulator date and a contract end date, but inside those we ran two week iterations with a demo, so the plan looked phased to the steering committee and felt iterative to the team. What I try hard to avoid is the worst of both, which is iterative delivery against a fixed detailed scope that was signed off eight months earlier.
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See how it worksFollow-up questions to expect
- How do you report iterative progress to a steering committee that expects a Gantt chart?
- What do you do when the organization mandates a methodology that does not fit?
- How do you handle fixed price contracts on uncertain scope?
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