This one took years to learn the hard way and I still routinely blow it to this day. It is not enough to be right, you also have to say the right thing, the right way and last but not least at the right time. If not the message is never heard by the way the messenger delivered it. Mark Merrill has a great post:
“No matter how nice you are, no matter how nice the people around you are, there will be times when you need to have a difficult conversation. Occasional tough talks are just a part of life. Maybe you have to talk with your spouse about a concern you have over something in your marriage.”