"The most common theory and all other theories about Nessie are likely not true" is the main idea of the passage. The author argues in the article that Nessie cannot be a plesiosaur or even real because there is no scientific evidence to support those theories. However, there is some proof that people are more likely to believe in something because someone at some prior point in time believed in it. Myths are very contagious and those with imaginations and a desire to believe will ignore common sense and science to believe in what they want.
