Usually the more a person has self-trust is the more relaxed he will be, when communicating with others. Most of the times when a person is not sure he is right or wrong he becomes more stressed and anger. This is the reason some people do not believe a person when he says anything while he has lots of anger feelings in his words.
Most of the times, when a person believes himself is capable to do a certain behaviour, he will not get nerves while doing it. Some people do no believe a person who over statements while he talks because if he really believes he is saying the truth, he should be calm because even if no one believes him but searched for other or opposite opinion, they will always come back to him. Usually defence is used if a person is feeling insecure but usually if he is sure he is right he will feel safe whether people attacks him( verbally ) or not.
Usually when a person is not sure of the things he is talking about and people start to ask him some questions, he searches ways to defend himself with. The more a person have self-confident or trust is the better for himself but he should be careful to prevent his self-confident from changing to ignorance. Most of the times a person’s confident is one of the reasons he becomes a successful person.