You've heard of build once, sell twice.
I don't know if I'm coining this but what the heck; Work now, sell later.
Building a SAAS product is almost all up front work, then you reap the benefits later. While writing my book I've come to realize this follows a similar principle. The work you do upfront holds massive power (In terms of ability to sell) similar to a SAAS product, but attracting people to buy that product is a whole other beast.
Thats why so many people are starting to build in public, it is a method to starting marketing at no extra cost and BEFORE you launch your SAAS product, book, etc.
Day 5 was successful: I'm starting to reap the benefits of previous days of building in public -> + 3 subscribers and +2 interviews booked.