You only use 10% percent of your brain.
James heard this folklore last year from his uncle who also lives in Kansas city. The topic came up as they were talking about James ability to study of the SAT. His uncle, Sam Meiners, told him this as a factual statement.
James said he also heard this same folklore when he was in fifth grade. It seemed to be a rumor that was going through the school at the time. He did believe it when he heard because he felt it would account for why some people are a lot smart than others, because somehow they had figured out how to use more of their brain. However, it wasnt until he talked to one of his high school teachers that he found out that it was in fact a myth and not actually a fact.
Folklore about the body seems to be more popular with younger children as they havent had the same education about biology that adults have had. For this reason, they make up answers for some of the bodies more confusing attributes like why there is such a great range of how smart people are.
For reference in text, see:
James, William. The Energies of Men. New York: Moffat, Yard and Co., 1907. Pg 12.