I've learned most people don't like to be told what to think or to be proved wrong. They have to come to the conclusion themselves. The way to do that is to question their beliefs and motives steering them to the answers but not giving them the answers directly. Let them by themselves figure out the correct answers. It's like anything else. If you're just given something, you're not going to appreciate its worth, but if you work for something, you will appreciate it more.