Ten percent myth

It's not true that humans only use ten percent of our brains. No study has ever shown or even claimed that. It's just something people say for no reason. The ten percent myth, probably the most common piece of neuro-mythology, is the pseudoscientific idea that humans only use ten percent of their brains (the number may be given as eleven, twelve, or thereabouts, but ten is most common). This idea is easily refuted by looking at a brain through any modern scanning technology, which shows that most parts of the brain will show some activity at any given time. This is why doctors never say, "It's okay, he was shot in the part of the brain that no one uses!" The idea was a prominent theme in the film Lucy (2014), which is painful to watch for anyone with a background in science. It is also easily refuted by the sheer amount of maintenance the brain requires; it wouldn't be beneficial for evolution if a useless part requires so much calories and nutrients.

The idea has been mis-attributed to various scientific figures, but most commonly William James and Albert Einstein. Some believe that the myth was a misreading of this line by James: We are making use of only a small part of our possible mental and physical resources. The ten percent myth is the basis for a good amount of woo. It often turns up in New Age tracts, especially those related to the Human Potential Movement. It's used to justify the existence of some "hidden" or "secret" powers of the brain that can be "unlocked," such as super-intelligence (or for them, even an average IQ), telepathy, telekinesis, psychic powers, etc. This suggests that New Age advocates may use only ten percent of their brains.

Note: It has been disputed in the past whether humans use their entire brain power, by the analogy that if you have a car that can drive at a maximum of 100 mph, and you drive at 10 mph, you are still using the entire engine, but not at its full power. This is definitely a valid point about the brains of creationists and such (as their brains are as powerful as everyone else's), but it is not known whether a rational person is operating their brain at its maximum possible power.