Non-violent Communication is a model of relating designed by Marshall Rosenberg. Although the model is vast, the basic principles are that people relate to each other by either asking for their needs to be met or saying thank you for having their needs met.
In essence he suggests we are either saying "Please" or "Thank you",
For anyone looking to enrich their relationships, with friends,co-workers or significant others we recommend learning more about Rosenberg's Non-Violent Communication.
There are many videos of Marshall Rosenberg online but the videos below are a good Introduction that simply state this theory :)