In his book "Practical Thinking", Dr. Edward de Bono talks about the basic thinking processes, how one understands, and the ways to be right or wrong in thinking. He said that the main purpose of thinking is not just to accumulate knowledge but also to get enough knowledge in order to act on something. He also said that, in practice, the validity of an idea does not have any bearing in being right in thinking, for being right is a feeling, a belief that one is right during the time of thinking.
To put this into practical use, you should write your ad copy so that your visitors will feel it is right to buy your products. Make them feel that it is their idea to make the purchase. By doing so, it will be easier for you to persuade these potential customers to hit that buy button.