Who is your first customer, and why?

More than once recently, I've found myself giving advice in the form of this question from a favorite professor: "Who is your first customer, and why?" This was something he posed to the class repeatedly, in the context of creating a go-to-market strategy for a startup. But these days -- or, heck, fifteen years ago -- what's good for a startup is also good for a person, and any project you might do.

So, it's a valuable question to ask when planning out a project: who is your first [ customer | user | reader | fraggle ], and why? It's natural and healthy to dream big and aim for a million users. But until the case is made to your investor (and yourself) that customer #1 is ready and willing, it's hard to believe that the throngs will follow.