How do you cook up an idea that's so plausible and appealing, yet completely mistaken? You start by misinterpreting the incomplete scientific knowledge of the time. Then, take a couple of esteemed men of science and misquote them.
In the 19th and early 20th centuries, medical researchers who studied the brains of animals and stroke victims discovered that different brain areas controlled different activities. In the 1870s, for example, German physiologists Gustav Fritsch and Eduard Hitzig electrically stimulated a spot in a dog's brain and noticed that the dog moved its right front paw. When they surgically removed that tissue from two other dogs, they noticed that the dogs not only couldn't use the paw, but seemed unaware of it [source: Finger]. Over the next half-century, other researchers eagerly zapped various parts of animal and human brains in an attempt to map brain function. But they were only able to figure out what about 10 percent of the brain did, because when they stimulated the other 90 percent, no muscles twitched. Scientists labeled that area the silent cortex because its function was unknown. We now know that's the area that, among other things, controls language and abstract thinking [source: Wanjek]. Non-scientists, however, mistakenly took this to mean that most of the human brain was on permanent vacation.
Through the miracle of misquotation, some celebrated minds also have helped promote the 10 percent brain myth. Pioneering psychologist-philosopher William James, wrote in a 1906 essay that he believed "we are only making use of a small part of our possible mental and physical resources" [source: James]. Journalist Lowell Thomas -- the same promotional genius who helped make Lawrence of Arabia into a legend -- tinkered with James' words to help market self-improvement guru Dale Carnegie's 1936 book "How to Win Friends and Influence People." In the book's forward, Thomas wrote that "the average person develops only 10 percent of his latent mental ability," and attributed that information to James [source: Carnegie].
Since then, other self-help authors have attributed the idea that we only use 10 percent of the brain's capacity to Albert Einstein -- a curious source, since his expertise was in physics, not neuroscience. In 2004, a thorough search by staffers of the Einstein archives at California Institute of Technology, however, found no evidence that he ever made such a statement [source: Beyerstein].