Being flexible does not help always. Thinking as if Kisor became so pessimist, not exactly I'm just making an adjustment in the trade-off point. I decided to be little rigid to make myself more efficient and make better use of resources. Here I remember one more point; people feel you are important when you reject them rather when you accept. A better trade-off between flexibility and rigidity is needed when you are going to lead/manage people, because the decision affects all the people in team not just you. The common goal is always more important than any individual contributor.
I have recently read two books FIRE SOMEONE TODAY and iCon which advocates this kind of philosophy.