Defensiveness as a response is the evidence that what someone says about you is based in a kernel of truth. When we are defensive it subtly proves our own acknowledgment of our own weaknesses.
If someone were to make a claim about you that were untrue and you had full confidence knowing it wasn’t true and you had conviction that the fruit of your life would demonstrate that the claim were untrue then what would be the need for defensiveness?
There would be no need for defensiveness for the right thing would be obvious. Lies do not hold up for long underneath the scrutiny of transparency. If your life and your choices and your reputation were a reflection of the opposite of what someone were to say about you, then their claim should not carry enough weight to emotionally impact you.
Rather, their claim would make them look like a fool. And you and everyone else would know that what they say were not true. There would be no validity to their challenge and so there would be no need to respond seriously to it. Time and a simple exploration of the facts would demonstrate the contrary of what they purport.
So then it is true that defensiveness is our reaction to a truth that someone points out that we do not want to admit. We are not proud of the weakness that we have that they have drawn attention to and so we are sensitive to it. We are ashamed that perhaps what they say is at least partially true. We have survived with that weakness by thinking that we can hide it. And so when it is exposed, it pierces into a painful place in our life that we have tried to hide. It is out of that sensitivity that we respond with defensiveness.
If you are defensive, if you are resistant, if you are sensitive to feedback that somebody is giving you it is because you know deep down that there is a truth in what they say.