Chapter five in Marvin Weisbord's Productive Workplaces opens with a quote from Edgar Schein, taken from The Professional Manager. It is worth sharing.
The essence of [McGregor's] message is that people react not to an objective world, but to a world fashioned out of their own perceptions, assumptions and theories about what the world is like....McGregor wished passionately to release all of us from this trap, by getting us to be aware of how each of our worlds is of our own making. Once we become aware we can choose - and it was the process of free choice that we believe was Doug's ultimate value.
After reading this, I purchased all three of Douglas McGregor's books on leadership. I'm sure I'll have more to share as I go through them.