Because people understand by finding in their memories the closest possible match to what they are hearing and use that match as the basis of comprehension, any new idea will be treated as a variant of something the listener has already thought of or heard. Agreement with a new idea means a listener has already had a similar thought and well appreciates that the speaker has recognized his idea. Disagreement means the opposite. Really new ideas are incomprehensible. The good news is that for some people, failure to comprehend is the beginning of understanding. For most, of course, it is the beginning of dismissal.