Launched: Interview to Find Product-Market Fit
After launch, interviews get a sharper aim: finding your way to product-market fit. Migicovsky points to the Superhuman approach from Rael Dornfest and Superhuman's Rahul Vohra: regularly ask users 'how would you feel if you could no longer use this product?' and track the percentage answering 'very disappointed.'
The magic threshold is roughly 40% very disappointed. Below it, keep iterating. The follow-up questions tell you where: ask the very-disappointed users what the product's core value is for them, and ask the merely somewhat-disappointed users what's missing. Build for the first group's reasons, informed by the second group's gaps.
This turns the fuzzy notion of product-market fit into a measurable loop: survey, segment, interview, iterate, survey again.
Key idea
Post-launch, measure fit: track the share of users who'd be very disappointed to lose you, and iterate toward 40% using their own words.