Affinity, Reality, and Communication are the three cornerstones of human communication. They are used by salespeople but we can apply them generally to other relationships since we are not capitalists. You should not use this to manipulate others or for self gain, but rather to figure out why relationships fail for you, or to determine how to interact well with others. The three principles of ARC are correlated to each other, and you will notice in many arguments where a lack of one leads to a rapid decrease in the other two corners of the ARC triangle. Failure of ARC usually leads to arguments but even if it does not, social interaction will not be as good as if ARC was present.
Affinity is the basis of respect and a liking for the other person. You will not like every person you interact with, but without affinity you are interacting with an enemy of some kind. Treating people well, appreciating them, and not raising your voice are ways to practice Affinity as well as generally being nice during conversations. It is the most basic of ARC and without it, there is a very low chance of having any kind of productive conversation.
Reality in ARC is about being able to agree on the same basis of reality. This does not mean you need to agree with everything as the other person, but you should obviously not say anything that will cause a break in the conversation or make the person question the reality of either them or yourself. Reality can be broken through seemingly mundane statements such as anything relating to sensitive topics. Reality can be damaged by disagreeing or making contradictory statements to what people believe but these are usually salvageable. Severe reality breaks are talking to people about mythical creatures or saying things that sound completely crazy to the other person, even if they are true to those who understand them. As spiritual people you will notice the uninitiated sometimes break reality with you if exposed to your knowledge.
Communication in ARC means clearly communicating thoughts and ideas. If you are practicing affinity and reality with a person you’re already doing a good job, but you must be able to communicate clearly to get across whatever you are trying to say. This does not matter as much in casual conversation with people you like, but a breakdown in communication will cause you to be unable to articulate words and you will just ramble, speak gibberish, or you will just make strange sounds with your mouth when you attempt to talk. Less severe cases of communication breakdown can also be caused by trying to explain things with overly complex vocabulary or trying to discuss topics that are too specific or difficult for people to understand. Being a poor communicator can also result from ambiguity or speaking in ways that leave you open to be misunderstood.
You can also sign off on communications with -ARC as some people do, but this would likely require you to explain all of this.