What is the most important quality in communication?
It is not clarity. It is not conviction or confidence. It is not about using the best words in a good order. It is not about body language or facial expression or power stances. It is not about vocal color.
All of those are important and, in some measure, necessary. But none of them have the same transformational impact on human communication as where you are coming from.
If you truly, sincerely, have a desire to listen, to be curious, to learn, to understand, to be or service and of contribution to another, everything else that appears to matter so much in communication will either take care of itself, or be taken care of by us in due course,
If you have any measure of a personal agenda to win, overcome, punish, fix, change, make someone wrong - you'll get the inevitable results of that. You'll find that you have triggered the other's desire to defend, avoid or lie to you.
Communication is a system. What you put in, you get out.