Opposition is a Sign of Involvement
In order to persuade someone to your way of thinking it is necessary that he first pass through a stage of resistance. The resistance arises from his having to give up the position he already has. He may listen to you, comprehend what you say, even do what you say. But listening or even complying for the moments doesn't necessarily mean that he accepts what you say. After all, he can do what you ask simply because he wants to please you, without necessarily adopting your ideas.
But taking over your ideas requires a readjustment of a number of other associated ideas he has. Your thinking has to be made to fit into the whole train of his associated thinking. And pressure on him to change his thinking is going to arouse some resistance.
If his mind were empty to begin with, he might readily accept your ideas. They would rush in to fill the vacuum. But people's mind are not empty. They have ideas and positions on just about everything. Even if many of these positions have never been put into words, they exist implicity, following from other ideas or feelings.
For example, suppose you were trying to persuade someone to go for an annual medical check-up. He may nod, agree that it's a good idea, and then not move to do anything about it. Within him is an oppositional force to this idea. He may be afraid of the findings. He may feel that there can't be anything wrong with him since if there were he would feel pain or experience some other symptom. He may shy away from the discomfort he anticipates from a thorough medical examination. And he might not want to spend the money or give up the time.
When you present to him the idea of yearly medical examinations he doesn't argue. He doesn't want to engage you in argument because he knows that on the basic of logic he would lose; and if logic were the basis of his action he would have to go. Therefore, he avoid engagement. He agrees. He gives lip service. He terminates discussion of the subject by giving outward indications of acceptance. In effect, he has cut off your channel of persuasion.
On the other hand, when he opposes you, marshals arguments contrary to yours, he leaves himself open to convincing. Now something within him is responding to your ideas. Some part of him feels that what you are saying makes sense and another part of him-the part that doesn't want to go-is fighting against your arguments. His resistance, his struggle to convince you of the opposite, is a sign that he is fully involved in considering your position. He isn't comfortablewith his own. He knows deep down that it doesn't make sense but fights to hold it anyway by trying to convince you as a way of convincing himself. In any case the channel of persuasion is open. He is responsive to your arguments even though the response at the moment is oppositional. One part of him is in conflict with another.