Most interview advice is about questions. The close gets a paragraph, usually something like "ask for a follow-up." That advice fails because it ignores what the conversation has been doing for the previous forty minutes.
A good interview is deliberately non-pitchy. You keep your idea out of it, ask about past behavior, and listen more than you talk, which is the core discipline of The Mom Test. Harvard's Rock Center puts it bluntly in its customer discovery guide: use interviews to discover and learn, not to validate your opinion or pitch. The trouble is that the moment the interview ends, you need something the conversation was never designed to produce: a next step.
So the close has to do two things at once. It must stay inside the discovery frame (no pitch, no demo, no "so what do you think of our approach?"), and it must convert goodwill into a scheduled, named, dated commitment. Those goals are not in conflict, but they feel like they are, which is why people either skip the close entirely or panic and start selling.
The second problem is measurement. Interviews produce false positives even when you avoid pitching. The Harvard guide flags exactly this: false positives occur when interviewers hear what they want and when people say what they want to hear. Rob Fitzpatrick's book exists to fix the same failure, described on the Mom Test site as a handbook for figuring out whether someone is really going to buy when everyone is being polite. A close that produces a verifiable artifact is the cheapest defense against that.



