I wish someone had given a copy of this book: the mom test, when I was starting up. It would have saved 1000 odd hours which as a team we consumed in meetings and shipping features.
As an early-stage company and a first-time founder, I have gone through many cycles. Sometimes misread what customer is saying irrespective of buying or feature requests.
If you or your friend is starting his own, give them a copy of this book. The book is all about asking the right questions from potential customers, understanding pain before writing a line of code.
We get so blinded with a few sets of conversations that we end up assuming a pain worth solving when there is none.
This book is going to be complementary with Jobs To be done book: when coffee kale compete.