This was reinforced to me many times when I was an attorney. I knew negotiators who would use it to gain advantages for their clients. It has many, broader applications. Use it to spot those easily controlled, and try to find out who's controlling them. Take it as a warning, and try to make it hard to offend you (forgiving people helps, as does remembering that you're no better than they).
Perhaps a moment to read a book: The Golden Sayings of Epictetus comes to mind. So does Proverbs 4:23 “Keep thy heart with all diligence; for out of it are the issues of life.” Shorter, but a bit more gnomic.