Can you walk through the product-market fit engine in practice?

We ask users four questions. The most important is how would you feel if you could no longer use the product, with options of very disappointed, somewhat disappointed, or not disappointed. If over 40 percent say very disappointed, you have product-market fit. In Superhuman Mail's early days we were at 22 percent, which is dangerously low. Within three quarters we got it to 58 percent by studying who was saying very disappointed, understanding what they loved and what was holding everyone else back, and then building toward the fans while removing the obstacles for everyone else.