The breakthrough? The thing that made a difference between smooth sailing and another series of phone calls?
A habit, really. I said, "Yes, sir" when confirming something. And he warmed up, and his questions became less hostile, and a different ending was aimed for. He wanted things to work out well for the person who called him "sir." I've had the same result from "Yes, ma'am" before, too. I don't remember it frequently enough for it to smooth all my paths, but considering its magical effects, I should. This is the kind of spell Harry Potter would be thrilled with: suddenly the muggles want him to win, rather than staying focused on themselves.
As a parent, therefore, one of my jobs, difficult as it is in the culture of Los Angeles, is to get my child to occasionally say, "Yes, sir." and "Yes, ma'am" and observe the effects. It is difficult because I am surrounded by adults who insist that they be treated like children, addressed by their first names on first acquaintance, as if their experience and understanding had frozen in high school. A little googling teaches me that sir and ma'am are controversialand there are people who carry it too far.