Neurologist and philosopher William James often told audiences that people only meet a fraction of their full mental potential. It is likely that he was speaking metaphorically.
In this book, a self-help advertisement contains the line "There is NO LIMIT to what the human brain can accomplish. Scientists and psychologists tell us we use only about TEN PERCENT of our brain power."
In the preface of Dale Carnegie's book "How to Win Friends and Influence People," Lowell Thomas summarized James's speeches by writing: "Professor William James of Harvard used to say that the average man develops only ten percent of his latent mental ability."
He wrote "that we might be using only five to ten percent of our mental capacity."
Deathstroke is said to be able to use 90% of his brainpower.
National magazine ads for Satellite Broadcasting showed drawings of the brain with a caption underneath that read: "You only use 11 percent of its potential."
Advertisements for the ABC show "The Secret Lives of Men" claimed that "Men only use ten percent of their brains."
Techno-thriller novel The Dark Fields by author Alan Glynn is based on the premise that we only use 20% of our brains and a pill could unlock the rest.
Limitless (starring Bradley Cooper) is a movie based on the novel The Dark Fields.
Lucy (starring Scarlett Johansson) is a science action film about a woman who gains superhuman abilities when she takes a drug that allows her to access 100% of her brain.
This TV show is based on the same concepts as the movie Limitless.