I too have been working on the "pick 2" rule mentioned by others here, for most of my adult life. Can't remember where/when I first ran into that rule. Maybe in my management training in the early 90s.

And I definitely agree, people are never a "commodity". Even a "would you like fries with that" type position in a company can be better served by some people than by others. Some will, just by attitude, body language, etc., encourage people to come back, while some will drive people away, even on something as simple as that.