There is a lot of 'common knowledge' around. Here's some from days-gone-by. The Earth is the center of the universe! The Earth is flat! Tomatoes are poisonous! Traveling at speeds in excess of 25 mph is inherently hazardous to your health! Some women practice witchcraft and must be burned at the stake! Yep! Each and every one of the above "factoids" was once common knowledge, and folks took them as gospel. What can you add?