"Ten Powerful Phrases for Positive People" by Rich DeVos who is the cofounder of Amway and the Chairman of the Orlando Magic. It's not a big book but it was a great read. There is no one this book would not benefit, especially coaches. This is a relationship-improvement book whether it's your professional life or your personal life. I will share some of these words and the thoughts but DeVos gives so many great stories that I strongly recommend you get the book.
#1: I'M WRONG
I chose to begin with “I’m wrong,” because it’s the hardest of the phrases to say and genuinely mean.
Saying “I’m wrong” is meaningless unless it comes from our heart, not just our lips. That often requires a genuine and profound change within ourselves, because we need to accept that we can be wrong.
Wrongs are inevitable, and denying their existence only crease arrogance and strife.
We waste energy when we hate someone rather than forgive him.