Where have you been? Where are you going? And why?
You avoid forcing your characters to march too steadily to the drumbeat of your artistic purpose. You leave some measure of real freedom for your characters to be themselves. And if minor characters show an inclination to become major characters, as they’re apt to do, you at least give them a shot at it, because in the world of fiction it may take many pages before you find out who the major characters really are, just as in the real world it may take you many years to find out that the stranger you talked to once for half an hour in the railroad station may have done more to point you to where your true homeland lies than your priest or your best friend or even your psychiatrist.