The "We Use Only 10 Percent of Our Brains" Myth
Some neuromyths take on life because the language of neuroscience is not familiar or easily translatable. This is certainly true with some of our own "eduspeak" (consider the reaction to phonemic awareness or summative feedback outside of a school). The neuromyth that we use only ten percent of our brainpower is beyond "lost in translation" -- it's a bad translation to begin with.
Some attribute the myth to mistranslations of mistranslations. In a book forward, journalist Lowell Thomas over-interpreted this statement written in the mid 1800s by William James, the father of modern psychology: "As a rule, men habitually use only a small part of their powers which they actually possess." Thomas made that generalization more concrete by: "Professor William James of Harvard used to say that the average person develops only ten per cent of his latent mental ability."
To clarify the science, consider that the brain weighs three pounds and uses about 20 percent of the body's limited oxygen and glucose resources. The brain has built-in efficiency systems to keep it trim -- it destroys unused or disconnected islands of brain connections. When networks are not activated frequently enough to build up the strong walls of myelin and multiple dendrite connections, they are pruned away, assuring more availability of metabolic resources for the most-used brain networks. Hence, we have "neurons that fire together" (the construction aspect of neuroplasticity) and its flipside, "use it or lose it.