It is rare to find a truly non defensive individual but where you do you have an easy person to talk to because they have intentionally developed an attitude of nothing to prove, nothing to lose.
If I have nothing to prove, I don't need to be right all the time, I don't need to have all the answers, and I have nothing to be defensive about when I receive a word of criticism or counsel. That does not mean that I must agree with the evaluation being shared but I can evaluate it from a more neutral position because I don't have anything to prove.
Those who have nothing to prove and nothing to lose have open faces that invite conversation and dialogue while those who are defensive have closed faces that say, "don't go there." One invites conversation, the other shuts conversation down - fast.
Defensiveness comes out of two core and unhealthy needs. The need to be right and the need to not lose "face." The need to be right is plain arrogance (none of us are always right) and the need to not lose "face" is simply our pride which is an artificial shell we erect around ourselves to project the image of something we are really not.
Both arrogance and pride are products of our lower nature, are routinely on the list of things God hates (see Proverbs) and are the root of defensive attitudes.
Healthy individuals intentionally cultivate an attitude of nothing to prove, nothing to lose. They are open to criticism or evaluation because they do not feel a need to prove anything and are comfortable enough in their own skin that they are not afraid of losing anything.
It is an attitude of healthy humility that comes out of an inner core of personal confidence, healthy self image and an open spirit. There is no hint of arrogance or pride - thus there is no personal defensiveness.
Think of the people you know well. Which of them respond with openness to suggestions or evaluation? Which of them bristle and shut down the conversation? How do you do in this area?
It is a good mantra to remember: Nothing to prove, nothing to lose.