Hi Peter, thanks for sharing this. I don’t see a particular misalignment with what I wrote and the Y-C post. What I mean by “clarifying the vision” is related to (to use the language of the post) the articulation of the riskiest assumptions in the project. I’ve seen many projects where the upfront vision is not articulated clearly enough to begin testing those assumptions.
That said, as much as folks would like to reduce this process to an analytical science, for these tests to be valid in practice they need to include a mix of assumptions. Testing individual assumptions on their own may not convey the whole picture to possible users. Some synthetic thinking is required upfront, and designers can be invaluable in this process.