[Jugurtha]

Ideally you'd have customers very early on for the very validation of your idea. Have a look entitled "Traction: How Any Startup Can Achieve Explosive Customer Growth" by Gabriel Weinberg (DuckDuckGo's founder) and Justin Mares.

Unordered, indexed, playlist: https://www.youtube.com/playlist?list=PLpNwgXYhL09_afXgVjigb...